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Diets for weight management in adults with type 2 diabetes: an umbrella review of published meta-analyses and systematic review of trials of diets for diabetes remission.
Churuangsuk, C, Hall, J, Reynolds, A, Griffin, SJ, Combet, E, Lean, MEJ
Diabetologia. 2022;65(1):14-36
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Type 2 diabetes (T2D) is a global epidemic. Although it is a complex disease, it is mainly driven by weight gain. The benefits of weight loss for T2D are well known, but patients and healthcare practitioners do not have clear guidance as to which dietary strategies may be effective to achieve and to maintain weight loss. The aim of this study is to review a number of studies of weight loss diets in T2D patients to see which ones are the most effective. Also, to see which dietary patterns support type 2 diabetes remission. Greatest weight loss was reported with very low energy diets including formula meal replacements. Low-carbohydrate diets were no better for weight loss than higher-carbohydrate/low-fat diets. High-protein, Mediterranean, high-monounsaturated-fatty-acid, vegetarian and low-glycaemic-index diets all achieved minimal or no difference from control diets. Diets for weight management in people with type 2 diabetes do not support any particular macronutrient profile or style over others. Very low energy diets and formula meal replacements appear to be the most effective. Programmes including a hypocaloric formula ‘total diet replacement’ induction phase were most effective for type 2 diabetes remission. Further research is needed to assess longer-term impacts on weight, glycaemic control, clinical outcomes and diabetes complications.
Expert Review
Conflicts of interest:
None
Take Home Message:
- Authors highlight current evidence on diets for T2D remission is limited but believe remission can be achieved if sufficient weight loss is maintained. The main contributor to HbA1c reduction and remission appears to be weight loss, irrespective of diet type
- Nice Guidelines highlight the remission of diabetes occurs when a patient no longer satisfies the diagnostic criteria, without receiving glucose-lowering medication. By 2019 in one UK GP practice 27% of the practice population with T2D who followed a LCD for 23 months, lost weight and lowered their HbA1c to 48 mmol/mol (NICE target range) in conjunction with prescribed medication
- This review highlights an opportunity for Nutritional Therapy Practitioners to successfully work with LCD approaches to support weight loss and improved HbA1c.
Evidence Category:
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A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
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B: Systematic reviews including RCTs of limited number
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C: Non-randomized trials, observational studies, narrative reviews
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D: Case-reports, evidence-based clinical findings
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E: Opinion piece, other
Summary Review:
- 19 meta-analyses (MA) on weight-loss diets, involving 23 primary trials were assessed using A Measurement Tool to Assess Systematic Reviews (AMSTAR) 2. Findings were synthesised by diet type and study quality (Cochrane Risk of Bias tool 2.0 and Risk Of Bias In Non-randomised Studies – of Interventions [ROBINS-I]) with GRADE applied
- Weight loss diets in the review included: Formula meal replacements (high quality, GRADE moderate) achieved 2.4 kg (95% CI −3.3, −1.4) greater weight loss over 12–52 weeks. Low-carbohydrate diets were no better for weight loss than higher-carbohydrate/low-fat diets (high quality, GRADE high). High-protein, Mediterranean, high-monounsaturated-fatty-acid, vegetarian and low-glycaemic-index diets all achieved minimal (0.3– 2 kg) or no difference from control diets (low to critically low quality, GRADE very low/moderate)
- Greatest weight loss was reported with very low energy diets (VLED), (400–500 kcal). However, this study found that low-carbohydrate diets (LCD) (21–70g of carbohydrate daily from1000–1500 kcal) were no better for weight loss than higher-carbohydrate/low-fat diets
- Time period of diets / length of observation / intervention: (1) Formula meal replacements (>12–52 wk), (2) LCDs ranged between (>8 wk to 4 years), (3) Very low energy diets (>8–12 wk), (4) High- protein (>4->8 wks), Mediterranean (>4->8 wk), high-monounsaturated-fatty-acid (>2wk), vegetarian (≥3wk) and low-glycaemic-index diets (≥6mo)
- Authors highlight weight reduction is fundamental for T2D management and remission
- This MA found that VLED and formula meal replacement appear the most effective approaches for weight management with T2D by providing less energy than self-administered food-based diets
- Potential pathophysiological mechanisms highlighted by authors are HbA1c reduction and remission which appear to be from weight loss, with only small differences between diet types assessed over 3–12 months, irrespective of diet type
- Study limitations: Many meta-analyses were of ‘low’ and ‘critically low’ AMSTAR 2 quality, predominantly through ‘no protocol reported’ (despite clear and sound methods) and no assessment of publication bias
- Most studies included European participants, such that findings may not be equally applicable to other ethnic and/or deprived communities. Durations of interventions varied, where weight regain is frequent over a longer period. Authors highlight evidence from clinical practice is needed to identify safe and effective approaches to achieve and maintain weight loss
- Authors highlight primary studies should use an RCT design, with data analyses conducted ‘blind’. They should define the intervention clearly (e.g., diets, physical activity, and behavioural and psychological support), and address separately the induction (usually 3–6 months) and maintenance (≥12 months)
- This research received no funding
- The authors declared no conflicts of interest.
Clinical practice applications:
- While this study found a variety of dietary compositions can be used effectively for weight management with T2D, VLED was successfully used to achieve remission for T2D
- Programmes with a ’total diet replacement’ induction phase were the most effective dietary approach for T2D remission (up to 61% of participants at 1 year).
Considerations for future research:
- Authors state future research should provide implementation with optimal support in real-life settings for weight loss, prevention of weight regain and remissions, rather than seek subtle differences from macronutrient compositions
- Future studies should report sufficient detail about macronutrient or micronutrient contents, or prescribed and reported energy intakes, including energy intake of nutrient-restricted diets.
Abstract
AIMS/HYPOTHESIS Weight reduction is fundamental for type 2 diabetes management and remission, but uncertainty exists over which diet type is best to achieve and maintain weight loss. We evaluated dietary approaches for weight loss, and remission, in people with type 2 diabetes to inform practice and clinical guidelines. METHODS First, we conducted a systematic review of published meta-analyses of RCTs of weight-loss diets. We searched MEDLINE (Ovid), PubMed, Web of Science and Cochrane Database of Systematic Reviews, up to 7 May 2021. We synthesised weight loss findings stratified by diet types and assessed meta-analyses quality with A Measurement Tool to Assess Systematic Reviews (AMSTAR) 2. We assessed certainty of pooled results of each meta-analysis using Grading of Recommendations, Assessment, Development and Evaluations (GRADE) (PROSPERO CRD42020169258). Second, we conducted a systematic review of any intervention studies reporting type 2 diabetes remission with weight-loss diets, in MEDLINE (via PubMed), Embase and Cochrane Central Register of Controlled Trials, up to 10 May 2021. Findings were synthesised by diet type and study quality (Cochrane Risk of Bias tool 2.0 and Risk Of Bias In Non-randomised Studies - of Interventions [ROBINS-I]), with GRADE applied (PROSPERO CRD42020208878). RESULTS We identified 19 meta-analyses of weight-loss diets, involving 2-23 primary trials (n = 100-1587), published 2013-2021. Twelve were 'critically low' or 'low' AMSTAR 2 quality, with seven 'high' quality. Greatest weight loss was reported with very low energy diets, 1.7-2.1 MJ/day (400-500 kcal) for 8-12 weeks (high-quality meta-analysis, GRADE low), achieving 6.6 kg (95% CI -9.5, -3.7) greater weight loss than low-energy diets (4.2-6.3 MJ/day [1000-1500 kcal]). Formula meal replacements (high quality, GRADE moderate) achieved 2.4 kg (95% CI -3.3, -1.4) greater weight loss over 12-52 weeks. Low-carbohydrate diets were no better for weight loss than higher-carbohydrate/low-fat diets (high quality, GRADE high). High-protein, Mediterranean, high-monounsaturated-fatty-acid, vegetarian and low-glycaemic-index diets all achieved minimal (0.3-2 kg) or no difference from control diets (low to critically low quality, GRADE very low/moderate). For type 2 diabetes remission, of 373 records, 16 met inclusion criteria. Remissions at 1 year were reported for a median 54% of participants in RCTs including initial low-energy total diet replacement (low-risk-of-bias study, GRADE high), and 11% and 15% for meal replacements and Mediterranean diets, respectively (some concerns for risk of bias in studies, GRADE moderate/low). For ketogenic/very low-carbohydrate and very low-energy food-based diets, the evidence for remission (20% and 22%, respectively) has serious and critical risk of bias, and GRADE certainty is very low. CONCLUSIONS/INTERPRETATION Published meta-analyses of hypocaloric diets for weight management in people with type 2 diabetes do not support any particular macronutrient profile or style over others. Very low energy diets and formula meal replacement appear the most effective approaches, generally providing less energy than self-administered food-based diets. Programmes including a hypocaloric formula 'total diet replacement' induction phase were most effective for type 2 diabetes remission. Most of the evidence is restricted to 1 year or less. Well-conducted research is needed to assess longer-term impacts on weight, glycaemic control, clinical outcomes and diabetes complications.
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Low-carbohydrate diets and men's cortisol and testosterone: Systematic review and meta-analysis.
Whittaker, J, Harris, M
Nutrition and health. 2022;28(4):543-554
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Testosterone is the primary male sex hormone, and vital for reproductive development and function. Moreover, low endogenous testosterone is associated with an increased risk of chronic disease, including type 2 diabetes and cardiovascular disease. The aim of this study was to investigate the effects of low- versus high-carbohydrate diets on mens' testosterone and cortisol. This study is a systematic review and meta-analysis of twenty-seven studies with a total of 309 participants. Twelve of these studies were randomised trials whilst the rest were non-randomised. Results show an increase in resting and post-exercise cortisol on short-term low-carbohydrate diets (<3 weeks). In fact, resting cortisol levels return to baseline after <3 weeks on a LC diet, whilst post-exercise cortisol remains elevated. Furthermore, high-protein diets cause a large decrease in resting total testosterone. Authors conclude that further research is required in order to warrant their findings.
Expert Review
Conflicts of interest:
None
Take Home Message:
- Short-term LC-diets diets cause a moderate increase in resting and post-exercise cortisol however this effect is not seen in LC-diets followed for great than 3 weeks
- HP-LC diets caused a statistically significant decrease in resting TT, suggesting caution in relation to endocrine effects of LC diets
Evidence Category:
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A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
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B: Systematic reviews including RCTs of limited number
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C: Non-randomized trials, observational studies, narrative reviews
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D: Case-reports, evidence-based clinical findings
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E: Opinion piece, other
Summary Review:
Introduction:
A systematic review and network meta-analysis was conducted on the effects of low-carbohydrate (LC) versus high-carbohydrate (HC) diets on men’s testosterone and cortisol.
The review was registered with PROSPERO and reported using PRISMA 2020 checklists.
Methods:
A comprehensive search strategy was used to find intervention studies looking at healthy adult males and LC diets of <35% carbohydrate. Studies were assessed for quality using the Cochrane Risk of Bias tool. Sub-group analyses was conducted for diet duration, protein intake and exercise duration.
Results:
The literature search resulted in 27 studies with a total of 309 healthy adult male participants, age: 27.3 ± 4.7 (to minimise variation in steroid hormone metabolism), body mass: 78.6± 7.1kg and BMI: 24.8 ±1.6. 12 randomised and 15 non-randomised controlled trials were analysed. 21 studies were considered low risk bias, 5 medium and 1 high risk.
- Short-term (<3 weeks) LC diets moderately increased resting cortisol (0.41 [0.16, 0.66], p < 0.01) when compared to HC diets.
- Long-term (≥3 weeks) LC diets had no consistent effect on resting cortisol
- LC diets resulted in higher post-exercise cortisol, after long-duration exercise (≥20 min): 0 h (0.78 [0.47, 1.1], p < 0.01), 1 h (0.81 [0.31, 1.31], p < 0.01), and 2 h (0.82 [0.33, 1.3], p < 0.01).
- The overall results for resting total testosterone (TT) showed a significant decrease on LC versus HC diets (SMD = −0.48, p = 0.01. However, subgroup analyses revealed this effect to be limited to high-protein (HP) LC diets, which yielded a very large decrease in TT (SMD = −1.08, p < 0.01; ∼5.23 nmol/L), albeit in a small sample (n = 26).
- Moderate protein (MP) (<35%), low-carbohydrate diets had no consistent effect on resting total testosterone, however high-protein (≥35%), low-carbohydrate diets greatly decreased resting (−1.08 [−1.67, −0.48], p < 0.01) and post-exercise total testosterone (−1.01 [−2, −0.01] p = 0.05).
- There was no overall effect of LC versus HC diets on 0 h post-exercise TT (SMD = −0.03, p = 0.95). However, subgroup analysis showed 0 h post-exercise was non-significantly higher on long-term LC versus HC diets (SMD = 0.44, p = 0.18), and much lower on short-term LC versus HC diets (SMD = −1.01, p = 0.05)
Conclusion:
This systematic review and metanalysis found an increase in resting and post-exercise cortisol on short-term LC diets. Cortisol does return to baseline in the first 3 weeks of a low-carbohydrate (LC) diet. The same response is, however, not seen in post-exercise cortisol, which remains elevated. In addition, the review showed that compared to moderate-protein diets, HP diets were found to cause a large decrease in resting and post-exercise TT (∼5.23 nmol/L).
Clinical practice applications:
The results of this review suggest that exercising whilst following a LC diet can increase cortisol in the short term, but not long-term. This suggests a period of diet adaptation. The effects of long-term LC diets on cardiovascular disease risk is uncertain and healthcare practitioners should monitor client responses and keep up-to-date with new research in this area
Since HP-LC diets were found to significantly decrease resting testosterone it highlights the need to ensure that protein intake does not exceed the urea cycle’s capacity due to potential adverse endocrine effects.
For clients where there is a desire to increase strength, power and hypertrophy, a MP-LC diet could be of benefit, as it showed potential to signal an increased anabolic state post exercise..
NB: Since the review only included a low number of studies and saw within these some heterogeneity that could not be explained, more research is needed before the paper’s findings can be conclusive. The above potential practice applications should therefore be seen as something to be mindful of when working with clients where cortisol and testosterone levels are relevant to their protocol.
Considerations for future research:
Future research should consider:
- Since LC diets have been shown to have a positive effect on health – decreased triglycerides, increased high density lipoprotein cholesterol and weight loss - future studies would benefit from including these markers so any positive and negative impacts can be monitored directly.
- Despite extensive analysis including sensitivity analysis to reduce bias and heterogeneity of the results, the paper highlights a need for further research to ensure consistency in key parameters e.g., exercise duration and intensity, carbohydrate supplements inclusion and period of dietary intervention. Since it was identified that HP-LP diets impact post exercise and resting TT, follow up studies would benefit from consistency in participants diets. This would help to reduce any potential confounding results.
Abstract
Background: Low-carbohydrate diets may have endocrine effects, although individual studies are conflicting. Therefore, a review was conducted on the effects of low- versus high-carbohydrate diets on men's testosterone and cortisol. Methods: The review was registered on PROSPERO (CRD42021255957). The inclusion criteria were: intervention study, healthy adult males, and low-carbohydrate diet: ≤35% carbohydrate. Eight databases were searched from conception to May 2021. Cochrane's risk of bias tool was used for quality assessment. Random-effects, meta-analyses using standardized mean differences and 95% confidence intervals, were performed with Review Manager. Subgroup analyses were conducted for diet duration, protein intake, and exercise duration. Results: Twenty-seven studies were included, with a total of 309 participants. Short-term (<3 weeks), low- versus high-carbohydrate diets moderately increased resting cortisol (0.41 [0.16, 0.66], p < 0.01). Whereas, long-term (≥3 weeks), low-carbohydrate diets had no consistent effect on resting cortisol. Low- versus high-carbohydrate diets resulted in much higher post-exercise cortisol, after long-duration exercise (≥20 min): 0 h (0.78 [0.47, 1.1], p < 0.01), 1 h (0.81 [0.31, 1.31], p < 0.01), and 2 h (0.82 [0.33, 1.3], p < 0.01). Moderate-protein (<35%), low-carbohydrate diets had no consistent effect on resting total testosterone, however high-protein (≥35%), low-carbohydrate diets greatly decreased resting (-1.08 [-1.67, -0.48], p < 0.01) and post-exercise total testosterone (-1.01 [-2, -0.01] p = 0.05). Conclusions: Resting and post-exercise cortisol increase during the first 3 weeks of a low-carbohydrate diet. Afterwards, resting cortisol appears to return to baseline, whilst post-exercise cortisol remains elevated. High-protein diets cause a large decrease in resting total testosterone (∼5.23 nmol/L).
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The Effect of Ketogenic Diet on Shared Risk Factors of Cardiovascular Disease and Cancer.
Mohammadifard, N, Haghighatdoost, F, Rahimlou, M, Rodrigues, APS, Gaskarei, MK, Okhovat, P, de Oliveira, C, Silveira, EA, Sarrafzadegan, N
Nutrients. 2022;14(17)
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Cardiovascular disease and cancer are major causes of mortality worldwide and share common pathophysiological mechanisms and risk factors. The ketogenic diet, a low-carbohydrate and high-fat diet, may alter metabolic pathways, potentially lowering the risk of developing these diseases. Specifically, the ketogenic diet improves energy metabolism by promoting the use of body ketones for energy production. This review examines the protective effects of the ketogenic diet in reducing cardiovascular disease and cancer risk and explores the underlying mechanisms. The ketogenic diet may suppress oxidative stress and inflammation while improving common risk factors such as obesity, hypertension, diabetes, and dyslipidaemia. It is important to conduct further rigorous studies to assess the long-term effects of the ketogenic diet. However, healthcare professionals can use these findings to understand the short-term benefits of the diet in managing metabolic abnormalities and reducing the risk of developing cardiovascular disease and cancer.
Abstract
Cardiovascular disease (CVD) and cancer are the first and second leading causes of death worldwide, respectively. Epidemiological evidence has demonstrated that the incidence of cancer is elevated in patients with CVD and vice versa. However, these conditions are usually regarded as separate events despite the presence of shared risk factors between both conditions, such as metabolic abnormalities and lifestyle. Cohort studies suggested that controlling for CVD risk factors may have an impact on cancer incidence. Therefore, it could be concluded that interventions that improve CVD and cancer shared risk factors may potentially be effective in preventing and treating both diseases. The ketogenic diet (KD), a low-carbohydrate and high-fat diet, has been widely prescribed in weight loss programs for metabolic abnormalities. Furthermore, recent research has investigated the effects of KD on the treatment of numerous diseases, including CVD and cancer, due to its role in promoting ketolysis, ketogenesis, and modifying many other metabolic pathways with potential favorable health effects. However, there is still great debate regarding prescribing KD in patients either with CVD or cancer. Considering the number of studies on this topic, there is a clear need to summarize potential mechanisms through which KD can improve cardiovascular health and control cell proliferation. In this review, we explained the history of KD, its types, and physiological effects and discussed how it could play a role in CVD and cancer treatment and prevention.
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Non-Systematic Review of Diet and Nutritional Risk Factors of Cardiovascular Disease in Obesity.
Rychter, AM, Ratajczak, AE, Zawada, A, Dobrowolska, A, Krela-Kaźmierczak, I
Nutrients. 2020;12(3)
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Nutrition is a major factor influencing obesity associated heart disease risk, however many people with this disease do not follow nutritional recommendations. This review of 155 studies aimed to summarise dietary aspects of heart disease prevention. The paper began by outlining the role of obesity through the development of other disorders that contribute to heart disease, such as type 2 diabetes, high blood pressure and blood sugar imbalance. The quantity and distribution of fat tissue also can contribute to heart disease risk, especially if it is located within the heart or around the major organs of the body. Dietary factors which can increase heart disease risk were described as an increased intake of processed foods, sugar, salt and certain fats and low intakes of fruit, vegetables, fibre, whole grains, beans and nuts. The Mediterranean diet, the dietary approaches to stop hypertension (DASH) diet, plant-based diets, the portfolio dietary pattern and low carbohydrate diets were all reviewed and although mixed results were stated for low carbohydrate diets, most of the diets reviewed reported improved heart disease outcomes. The role of intestinal microbiota in heart disease were also reviewed and the influence of a poor diet was implicated in imbalanced gut microbiota and the development of heart disease. It was concluded that an unhealthy diet can contribute to heart disease and that dietary patterns such as the Mediterranean diet and plant-based diets may be favourable for its management. This study could be used by healthcare professionals to individualise dietary recommendations for patients with heart disease or who are at risk of it.
Abstract
Although cardiovascular disease and its risk factors have been widely studied and new methods of diagnosis and treatment have been developed and implemented, the morbidity and mortality levels are still rising-cardiovascular disease is responsible for more than four million deaths each year in Europe alone. Even though nutrition is classified as one of the main and changeable risk factors, the quality of the diet in the majority of people does not follow the recommendations essential for prevention of obesity and cardiovascular disease. It demonstrates the need for better nutritional education in cardiovascular disease prevention and treatment, and the need to emphasize dietary components most relevant in cardiovascular disease. In our non-systematic review, we summarize the most recent knowledge about nutritional risk and prevention in cardiovascular disease and obesity.
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Dietary Patterns in Secondary Prevention of Heart Failure: A Systematic Review.
Dos Reis Padilha, G, Sanches Machado d'Almeida, K, Ronchi Spillere, S, Corrêa Souza, G
Nutrients. 2018;10(7)
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Diet is recognised as an important factor in the prevention of heart failure, however there is no consensus about which dietary protocol is the most effective. This systematic review aims to clarify links between different dietary measures and markers of heart failure. The review included 12 studies of different types (randomised controlled trials, cross-sectional studies and cohort studies), which examined the DASH diet, Mediterranean diet, high protein diet and low carbohydrate diet. The studies examining the DASH diet demonstrated improvements in various measures of cardiac function and may have benefits for secondary prevention of heart failure. The Mediterranean diet was associated with lower levels of inflammation and improved cardiac function in cross-sectional studies only. High protein and low carbohydrate diets also demonstrated positive effects on markers of heart function however, only one study for each was included. The authors conclude that the current science suggests a positive role for diet in relation to prevention of heart failure and call for further RCTs to be conducted to identify which elements of these different diets are impacting on markers of heart failure.
Abstract
BACKGROUND Diet is an important factor in secondary prevention of heart failure (HF) but there is still no consensus as to which dietary model should be adopted by this population. This systematic review aims to clarify the relationship between dietary patterns and secondary prevention in HF. METHODS We searched the Medline, Embase and Cochrane databases for studies with different dietary patterns and outcomes of secondary prevention in HF. No limitation was used in the search. RESULTS 1119 articles were identified, 12 met the inclusion criteria. Studies with Dietary Approaches to Stop Hypertension (DASH), Mediterranean, Hyperproteic and Low-carb diets were found. The DASH pattern showed improvement in cardiac function, functional capacity, blood pressure, oxidative stress and mortality. The Mediterranean diet had a correlation with inflammation, quality of life and cardiac function but just on cross-sectional studies. Regarding the Hyperproteic and Low-carb diets only one study was found with each pattern and both were able to improve functional capacity in patients with HF. CONCLUSIONS DASH pattern may have benefits in the secondary prevention of HF. The Mediterranean diet demonstrated positive correlation with factors of secondary prevention of HF but need more RCTs and cohort studies to confirm these effects. In addition, the Hyperproteic and Low-carb diets, despite the lack of studies, also demonstrated positive effects on the functional capacity in patients with HF.
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Low-carbohydrate diets for type 1 diabetes mellitus: A systematic review.
Turton, JL, Raab, R, Rooney, KB
PloS one. 2018;13(3):e0194987
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Type 1 diabetes is an autoimmune condition that affects the ability to produce insulin, the hormone that regulates blood sugar levels. Patients with Type 1 diabetes manage their condition with daily insulin injections or patches, and the standard dietary advice is to continue to eat a normal diet, and adjust the insulin dose to keep blood sugar under control. This systematic review of 9 studies of varying types, aimed to examine the effects of low-carbohydrate diets on type 1 diabetes management. 8 of the studies reported a change in HbA1c (the blood marker used to assess long-term blood sugar management); 3 of these reported statistically significant reductions. 2 studies reported statistically significant reductions in daily insulin use whilst following a low-carbohydrate diet. The study authors were unable to conclude an overall effect due to the differences in design and methods used in the 9 studies included. They call for more primary research to be conducted.
Abstract
Type 1 diabetes is an autoimmune condition characterised by pancreatic beta cell destruction and absolute insulin deficiency. The strongest predictor of diabetes complications is glycaemic control and achieving HbA1c ≤ 7.0% is the primary management target. However, standard treatment appears to be lacking and adjunctive strategies require consideration. A systematic review was conducted to examine the effect of low-carbohydrate diets on type 1 diabetes management. Four databases were searched from inception until 28 March 2017: MEDLINE; CINAHL; Cochrane Library; and EMBASE. All primary studies containing a methods section (excluding cross-sectional) were included. Reports had to quantitatively measure the effect(s) of a dietary intervention or observed intake over at least two weeks where carbohydrate is below 45% total energy in adults and/or children with type 1 diabetes. The primary outcome was HbA1c and secondary outcomes were severe hypoglycaemia, total daily insulin, BMI, quality of life and mean daily glucose. Seventy-nine full-text articles were assessed for eligibility and nine were included (two randomised controlled trials, four pre-post interventions, two case-series, one case-report). Eight studies reported a mean change in HbA1c with a low-carbohydrate diet. Of these, four reported a non-significant change (P ≥ 0.05) and three reported statistically significant reductions (P < 0.05). Two studies reported severe hypoglycaemia, five reported total insulin, three reported BMI, and one reported blood glucose. Due to the significant heterogeneity of included studies, an overall effect could not be determined. This review presents all available evidence on low-carbohydrate diets for type 1 diabetes and suggests an urgent need for more primary studies.
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Does high-carbohydrate intake lead to increased risk of obesity? A systematic review and meta-analysis.
Sartorius, K, Sartorius, B, Madiba, TE, Stefan, C
BMJ open. 2018;8(2):e018449
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As overweight and obesity is rising globally, better understanding its cause is important to help with prevention and management of disease. The objective of this meta-analysis is to investigate the relationship between carbohydrate intake and obesity, particularly at the differences between low and high carbohydrate diets. Based on 22 articles that met the inclusion criteria, a high-carbohydrate diet, or increased proportion of energy intake in the form of carbohydrates, does not increase the risk of being obese. Based on these results, the authors iterate further studies are required to better understand obesity risk with regards different carbohydrate groups including refined versus unrefined carbohydrates.
Abstract
OBJECTIVES The present study aimed to test the association between high and low carbohydrate diets and obesity, and second, to test the link between total carbohydrate intake (as a percentage of total energy intake) and obesity. SETTING, PARTICIPANTS AND OUTCOME MEASURES We sought MEDLINE, PubMed and Google Scholar for observation studies published between January 1990 and December 2016 assessing an association between obesity and high-carbohydrate intake. Two independent reviewers selected candidate studies, extracted data and assessed study quality. RESULTS The study identified 22 articles that fulfilled the inclusion and exclusion criteria and quantified an association between carbohydrate intake and obesity. The first pooled strata (high-carbohydrate versus low-carbohydrate intake) suggested a weak increased risk of obesity. The second pooled strata (increasing percentage of total carbohydrate intake in daily diet) showed a weak decreased risk of obesity. Both these pooled strata estimates were, however, not statistically significant. CONCLUSIONS On the basis of the current study, it cannot be concluded that a high-carbohydrate diet or increased percentage of total energy intake in the form of carbohydrates increases the odds of obesity. A central limitation of the study was the non-standard classification of dietary intake across the studies, as well as confounders like total energy intake, activity levels, age and gender. Further studies are needed that specifically classify refined versus unrefined carbohydrate intake, as well as studies that investigate the relationship between high fat, high unrefined carbohydrate-sugar diets. PROSPERO REGISTRATION NUMBER CRD42015023257.
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Effects of Popular Diets without Specific Calorie Targets on Weight Loss Outcomes: Systematic Review of Findings from Clinical Trials.
Anton, SD, Hida, A, Heekin, K, Sowalsky, K, Karabetian, C, Mutchie, H, Leeuwenburgh, C, Manini, TM, Barnett, TE
Nutrients. 2017;9(8)
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Calorie-restricted diets have not been highly successful in reducing obesity levels. This has led to an increased interest in alternative dietary approaches to achieve sustained weight loss. The purpose of this systematic review was to analyse the most popular diets of 2016 for short- and long-term weight loss outcomes based on findings from clinical trials that do not include calorie restriction or increased physical activity levels. Of all existing literature, only 16 articles met the inclusion criteria covering 7 popular diets, indicating the lack of clinical trials and high-quality evidence. The Atkins diet is the most well-researched popular diet and demonstrates substantial long-term weight loss. The Paleolithic diet has also been found to produce sustained weight loss according to the one study included on this diet. Based to these findings, the authors conclude that of the popular diets, those with a low carbohydrate component seem to be effective, though the safety of these diets has not been critically examined. Further evidence is needed to provide a more comprehensive evaluation of the efficacy of each of these popular diets.
Abstract
The present review examined the evidence base for current popular diets, as listed in the 2016 U.S. News & World Report, on short-term (≤six months) and long-term (≥one year) weight loss outcomes in overweight and obese adults. For the present review, all diets in the 2016 U.S. News & World Report Rankings for "Best Weight-Loss Diets", which did not involve specific calorie targets, meal replacements, supplementation with commercial products, and/or were not categorized as "low-calorie" diets were examined. Of the 38 popular diets listed in the U.S. News & World Report, 20 met our pre-defined criteria. Literature searches were conducted through PubMed, Cochrane Library, and Web of Science using preset key terms to identify all relevant clinical trials for these 20 diets. A total of 16 articles were identified which reported findings of clinical trials for seven of these 20 diets: (1) Atkins; (2) Dietary Approaches to Stop Hypertension (DASH); (3) Glycemic-Index; (4) Mediterranean; (5) Ornish; (6) Paleolithic; and (7) Zone. Of the diets evaluated, the Atkins Diet showed the most evidence in producing clinically meaningful short-term (≤six months) and long-term (≥one-year) weight loss. Other popular diets may be equally or even more effective at producing weight loss, but this is unknown at the present time since there is a paucity of studies on these diets.
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Diet Behavior Change Techniques in Type 2 Diabetes: A Systematic Review and Meta-analysis.
Cradock, KA, ÓLaighin, G, Finucane, FM, McKay, R, Quinlan, LR, Martin Ginis, KA, Gainforth, HL
Diabetes care. 2017;40(12):1800-1810
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Plain language summary
Dietary behaviour is intrinsically linked to type 2 diabetes. Dietary factors have been linked to the highest proportion of deaths in type 2 diabetes, stroke, and heart disease. Identifying effective ways to help suffers successfully change to more effective dietary behaviours may help condition management and reduce disease progression. The objective of the systemic review and meta-analysis was to identify dietary behaviour change techniques, intervention features, and specific diets associated with changes in blood glucose levels (HbA1c) and body weight in type 2 diabetes. It included 54 studies, all of whose participants have type 2 diabetes. High-protein diets and meal replacement programs produced the greatest reductions in blood glucose (measured by HbA1c). Behavioural change techniques including 'problem solving,' 'feedback on behaviour,' 'adding objects to the environment' and 'social comparison' as well as interventions that were build on behavioural change theory were associated with clinically significant reductions in blood glucose as measured by HbA1c (a reduction of ≥0.3% (3.3 mmol/mol). However, the findings show that changing or controlling (e.g. providing all food) dietary environmental factors may be more effective than strategies to change dietary behaviour to reduce blood glucose levels in adults with type 2 diabetes. The authors conclude that changing the dietary environment may be more important than focusing on dietary behaviour in type 2 diabetes treatment.
Abstract
OBJECTIVE Dietary behavior is closely connected to type 2 diabetes. The purpose of this meta-analysis was to identify behavior change techniques (BCTs) and specific components of dietary interventions for patients with type 2 diabetes associated with changes in HbA1c and body weight. RESEARCH DESIGN AND METHODS The Cochrane Library, CINAHL, Embase, PubMed, PsycINFO, and Scopus databases were searched. Reports of randomized controlled trials published during 1975-2017 that focused on changing dietary behavior were selected, and methodological rigor, use of BCTs, and fidelity and intervention features were evaluated. RESULTS In total, 54 studies were included, with 42 different BCTs applied and an average of 7 BCTs used per study. Four BCTs-"problem solving," "feedback on behavior," "adding objects to the environment," and "social comparison"-and the intervention feature "use of theory" were associated with >0.3% (3.3 mmol/mol) reduction in HbA1c. Meta-analysis revealed that studies that aimed to control or change the environment showed a greater reduction in HbA1c of 0.5% (5.5 mmol/mol) (95% CI -0.65, -0.34), compared with 0.32% (3.5 mmol/mol) (95% CI -0.40, -0.23) for studies that aimed to change behavior. Limitations of our study were the heterogeneity of dietary interventions and poor quality of reporting of BCTs. CONCLUSIONS This study provides evidence that changing the dietary environment may have more of an effect on HbA1c in adults with type 2 diabetes than changing dietary behavior. Diet interventions achieved clinically significant reductions in HbA1c, although initial reductions in body weight diminished over time. If appropriate BCTs and theory are applied, dietary interventions may result in better glucose control.