Effects of Vegetable Consumption on Weight Loss: A Review of the Evidence with Implications for Design of Randomized Controlled Trials

Adherence to a vegetable dietary pattern attenuates the risk of non-alcoholic fatty liver disease in incident type 2 diabetes: The TCLSIH cohort study

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a strong risk factor for type 2 diabetes. However, no study has investigated whether dietary intake can modify this effect. Therefore, we aimed to investigate the effect of dietary pattern modification on the association between NAFLD and type 2 diabetes.

METHODS

A large prospective cohort study (n = 24,602) was conducted in China. NAFLD was diagnosed using liver ultrasonography considering alcohol consumption. Dietary data were assessed using a validated self-administered food frequency questionnaire. Cox proportional hazards regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Following a 93,873 person-year follow-up, 787 (3.20%) participants developed type 2 diabetes. In a multivariable adjusted model, compared with participants without NAFLD, the HR (95% CI) of incident type 2 diabetes for NAFLD patients was 3.04 (2.51, 3.68). On subgroup analyses, the adjusted HRs (95% CIs) of incident type 2 diabetes for NAFLD patients with low (≤median score) and high (>median score) vegetable pattern intakes were 4.08 (3.05, 5.46) and 2.38 (1.85, 3.07) (p for interaction <0.01), respectively. Higher vegetable intake was also found to attenuate the risk effect of phenotype groups of NAFLD on incident type 2 diabetes, especially in the lean NAFLD group.

CONCLUSIONS

The present study demonstrated that NAFLD is a strong risk factor for type 2 diabetes in the Chinese population. Notably, adherence to a dietary pattern rich in vegetables can attenuate this risk, especially in lean NAFLD patients.

Changes in vegetable and fruit intakes and effects on anthropometric outcomes in males and females

AIM

To investigate associations between changes in vegetable and fruit (V&F) intakes and anthropometric indices (weight, BMI, % body fat, waist circumference), including differences by sex, during a dietary weight-loss intervention.

METHODS

Adults (18-45 years) with overweight/obesity (BMI 25-35 kg/m² ) entered a 10-week pre-post study, receiving individualised consults with an Accredited Practising Dietitian targeting increased V&F intakes. Dietary intake was assessed using 24-hour recalls and food frequency questionnaires. Linear mixed models were used to examine how much of the changes in anthropometric indices were explained by changes in V&F intakes. Sex differences were assessed by Wilcoxon rank sum tests.

RESULTS

Of the 43 participants enrolled, 34 completed the study (53% female). Significant differences in energy intake and anthropometric indices were observed between males and females at baseline. After 10 weeks, females significantly reduced their weight (-2.9%, P < .01), BMI (-0.82 kg/m² , P < .01), waist circumference (-1.70 cm, P < .01), energy intake (-824 kJ/day, P = .01) and improved diet quality (-14.0% energy-dense, nutrient-poor foods, P < .01). Males significantly reduced weight (-2.5%, P = .04), BMI (-0.76 kg/m² , P = .03), waist circumference (-2.40 cm, P = .02), energy intake (-2875 kJ/day, P < .01), increased fruit intake (+0.89 serves/day, P = .02) and improved diet quality (-6% energy-dense, nutrient-poor foods, P < .01). Compared to the other sex, greater reductions were observed in energy intake in males and energy-dense, nutrient-poor foods in females. Linear mixed models identified that changes in V&F intakes did not explain the variation in anthropometric measures.

CONCLUSION

Future interventions may benefit from trialling sex tailored messages to enhance effects on anthropometric changes.

A Comprehensive Critical Assessment of Increased Fruit and Vegetable Intake on Weight Loss in Women

No previous reviews or meta-analyses have specifically assessed the effects of increased fruit and vegetable (FV) intake on weight loss with a primary focus on women. Several studies show differences between men and women in how increased FV intake affects their weight loss and maintenance, risk of becoming overweight or obese, and the influence of eating speed and frequency on weight control. This analysis provides a comprehensive and visual assessment of the effects of increasing FV intake and long-term weight change from observational studies and weight loss from randomized controlled trials (RCTs) in women. Consistent evidence from prospective studies and RCTs shows that increased intake of FV is a chief contributor to weight loss in women. This effect is enhanced with concurrent dietary restriction of high energy density (ED) or high-fat foods. Yet, the type of FV differentially impacts weight loss in women. Whole FV intake may influence weight through a variety of mechanisms including a reduction in eating rate, providing a satisfying, very-low to low energy density, low glycemic load or low-fat content. Also, FV are the primary source of dietary fiber, which can provide additional support for weight loss in women when consumed at adequate levels.

Global Vegetable Intake and Supply Compared to Recommendations: A Systematic Review

Low vegetable intake is associated with higher incidence of noncommunicable diseases. Data on global vegetable intake excluding legumes and potatoes is currently lacking. A systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was conducted to assess vegetable consumption and supply in adult populations and to compare these data to the existing recommendations (≥240 g/day according to World Health Organization). For vegetable intake data online, websites of government institutions and health authorities, European Food Safety Authority (EFSA) Comprehensive European Food Consumption Database, STEPwise approach to surveillance (STEPS) and Pubmed/Medline databases were searched from March 2018 to June 2019. Vegetable supply data was extracted from Food Balance Sheets, Food and Agriculture Organization Corporate Statistical Database (FAOSTAT), 2013. Vegetable intake was expressed as means and 95% confidence intervals. Data were summarized for each region by calculating weighted means. Vegetable intake and supply data were available for 162 and 136 countries, respectively. Weighted mean vegetable intake was 186 g/day (56-349 g/day). Weighted mean vegetable supply was 431 g/day (71-882 g/day). For 88% of the countries vegetable intake was below the recommendations. Public health campaigns are required to encourage vegetable consumption worldwide. In the 61% of the countries where vegetable supply is currently insufficient to meet the recommendations, innovative food system approaches to improve yields and decrease post-harvest losses are imperative.

The Relationship between Vegetable Intake and Weight Outcomes: A Systematic Review of Cohort Studies

The relationship between vegetable consumption and measures of adiposity was assessed in cohort studies. Seven databases were searched from inception until February 2018. The quality of individual studies was assessed using the Joanna Briggs Institute Critical Appraisal of Cohort Studies tool. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was applied to determine the quality of the body of evidence. Ten studies were included. Six measured change in vegetable intake over time. Two showed that increasing vegetable consumption resulted in weight loss of 0.09⁻0.1 kg over four years (p < 0.001). Increased vegetable intake was also associated with a reduced risk of weight gain and overweight or obesity (Odds ratios (ORs) ranged from 0.18 to 0.88) in other studies. Four studies measured vegetable intake at the baseline only. One showed that intakes >4 servings/day reduced the risk of weight gain (OR 0.27 (95% confidence interval (CI) 0.08⁻0.99) and another found an inverse association with waist circumference in women (-0.36 cm per vegetable serving/day). This review provides moderate quality evidence for an inverse association between vegetable intake and weight-related outcomes in adults. When these findings are coupled with no apparent harm from vegetable consumption, the evidence-base can be used with acceptable confidence to guide practice and policy.

Identifying usual food choices at meals in overweight and obese study volunteers: implications for dietary advice

Understanding food choices made for meals in overweight and obese individuals may aid strategies for weight loss tailored to their eating habits. However, limited studies have explored food choices at meal occasions. The aim of this study was to identify the usual food choices for meals of overweight and obese volunteers for a weight-loss trial. A cross-sectional analysis was performed using screening diet history data from a 12-month weight-loss trial (the HealthTrack study). A descriptive data mining tool, the Apriori algorithm of association rules, was applied to identify food choices at meal occasions using a nested hierarchical food group classification system. Overall, 432 breakfasts, 428 lunches, 432 dinners and 433 others (meals) were identified from the intake data (n 433 participants). A total of 142 items of closely related food clusters were identified at three food group levels. At the first sub-food group level, bread emerged as central to food combinations at lunch, but unprocessed meat appeared for this at dinner. The dinner meal was characterised by more varieties of vegetables and of foods in general. The definitions of food groups played a pivotal role in identifying food choice patterns at main meals. Given the large number of foods available, having an understanding of eating patterns in which key foods drive overall meal content can help translate and develop novel dietary strategies for weight loss at the individual level.

The effect of nut consumption on markers of inflammation and endothelial function: a systematic review and meta-analysis of randomised controlled trials

OBJECTIVES

To examine the effect of nut consumption on inflammatory biomarkers and endothelial function.

DESIGN

A systematic review and meta-analysis.

DATA SOURCES

MEDLINE, PubMed, Cumulative Index to Nursing and Allied Health Literature and Cochrane Central Register of Controlled Trials (all years to 13 January 2017).

ELIGIBILITY CRITERIA

Randomised controlled trials (with a duration of 3 weeks or more) or prospective cohort designs conducted in adults; studies assessing the effect of consumption of tree nuts or peanuts on C-reactive protein (CRP), adiponectin, tumour necrosis factor alpha, interleukin-6, intercellular adhesion molecule 1, vascular cell adhesion protein 1 and flow-mediated dilation (FMD).

DATA EXTRACTION AND ANALYSIS

Relevant data were extracted for summary tables and analyses by two independent researchers. Random effects meta-analyses were conducted to explore weighted mean differences (WMD) in change or final mean values for each outcome.

RESULTS

A total of 32 studies (all randomised controlled trials) were included in the review. The effect of nut consumption on FMD was explored in nine strata from eight studies (involving 652 participants), with consumption of nuts resulting in significant improvements in FMD (WMD: 0.79%(95% CI 0.35 to 1.23)). Nut consumption resulted in small, non-significant differences in CRP (WMD: -0.01 mg/L (95% CI -0.06 to 0.03)) (26 strata from 25 studies), although sensitivity analyses suggest results for CRP may have been influenced by two individual studies. Small, non-significant differences were also found for other biomarkers of inflammation.

CONCLUSIONS

This systematic review and meta-analysis of the effects of nut consumption on inflammation and endothelial function found evidence for favourable effects on FMD, a measure of endothelial function. Non-significant changes in other biomarkers indicate a lack of consistent evidence for effects of nut consumption on inflammation. The findings of this analysis suggest a need for more research in this area, with a particular focus on randomised controlled trials.

PROSPERO REGISTRATION NUMBER

CRD42016045424.

Impact of providing walnut samples in a lifestyle intervention for weight loss: a secondary analysis of the HealthTrack trial

Background: Being more specific about individual food choices may be advantageous for weight loss. Including a healthy food (e.g. walnuts) may help to expose effects.

Objective: To examine the impact of including walnuts in diets for weight loss.

Design: Secondary analysis of the HealthTrack lifestyle intervention trial. Overweight and obese participants were randomized to: usual care (C), interdisciplinary intervention including individualized dietary advice (I), or interdisciplinary intervention including 30 g walnuts/day (IW). Changes in body weight, energy intake, intake of key foods, physical activity, and mental health over three and 12 months were explored.

Results: A total of 293 participants completed the intensive three-month study period, and 175 had data available at 12 months. The IW group achieved the greatest weight loss at three months. IW reported significant improvements in healthy food choices, and decreased intakes of discretionary foods/beverages, compared to C. Weight loss remained greatest in IW at 12 months.

Discussion: Significant effects were seen after three months, with the IW group achieving greater weight loss and more favorable changes in food choices.

Conclusions: Including 30 grams walnuts/day in an individualized diet produced weight loss and positive changes in food choice.

A systematic review of food composition tools used for determining dietary polyphenol intake in estimated intake studies

Translating food intake data into phytochemical outcomes is a crucial step in investigating potential health benefits. The aim of this review was to examine the tools for determining dietary-derived polyphenol intakes for estimated intake studies. Published studies from 2004 to 2014 reporting polyphenol food composition information were sourced with 157 studies included. Six polyphenol subclasses were identified. One quarter of studies (n=39) reported total flavonoids intake with 27% reporting individual flavonoid compounds. Assessing multiple compounds was common with approximately 10% of studies assessing seven (n=13), six (n=12) and five (n=14) subclasses of polyphenol. There was no pattern between reported flavonoids compounds and subclass studied. Approximately 60% of studies relied on publicly accessible food composition data to estimate dietary polyphenols intake with 33% using two or more tools. This review highlights the importance of publicly accessible composition databases for estimating polyphenol intake and provides a reference for tools available globally.

Weight-Related Dietary Behaviors in Young Adults

The origins of the obesogenic environment date back to the early 1980s. This means that young adults i.e., those aged 18 to 35 years, have only ever experienced a food milieu that promotes obesity. Indeed, younger generations are becoming heavier sooner than their parents in developed countries, such as the USA. Young adults demonstrate food consumption patterns and dietary behaviors implicated in an excessive gain of body fat. They are the highest consumers of fast food and sugar-sweetened beverages among adult age groups and the lowest consumers of fruit and vegetables. Younger adults are meal skippers but may consume more energy from snacks than older adults. So that the gains made in stemming obesity in childhood are not undone during young adulthood, prevention programs are needed. This review highlights areas for consideration in planning such programs.

Impact of food supplementation on weight loss in randomised-controlled dietary intervention trials: a systematic review and meta-analysis

Dietary trials provide evidence for practice and policy guidelines, but poor adherence may confound results. Food supplementation may improve adherence to dietary interventions, but the impact of supplementation on study outcomes is not known. The aim of this review was to examine the impact of food supplementation on weight loss in dietary intervention trials. The databases Scopus, PubMed and the Cochrane Library were searched for dietary intervention trials published between January 2004 and March 2015 using the following keyword combinations: ‘trial’ OR ‘intervention’, ‘food’ OR ‘diet’, ‘weight loss’ and ‘adherence’ OR ‘adherence’. Studies were included if food was provided to at least one study group and both ‘weight change’ and ‘adherence’ were reported. Random effects meta-analyses were conducted to assess weighted mean differences (WMD) in body weight (change or final mean values). The included studies formed two groups: trials involving an intervention group supplemented with a food and a control without food supplementation (food v. no food), and trials in which food was provided to all subjects (food v. food) (PROSPERO registration: CRD42015017563). In total, sixteen studies were included. Significant weight reduction was reported in the food v. no food studies (WMD −0·74 kg; 95 % CI −1·40, −0·08; P=0·03, I2=63 %). A non-significant increase in weight was found among the food v. food studies (WMD 0·84 kg; 95 % CI −0·60, 2·27; P=0·25, I2=0 %). Food supplementation appeared to result in greater weight loss in dietary trials. Energy restrictions and intensity of interventions were other significant factors influencing weight loss.

Nutrition Promotion to Prevent Obesity in Young Adults

Young adulthood is a vulnerable period for weight gain and the health consequences of becoming obese during this life-stage of serious concern. Some unhealthy dietary habits are typical of young adults in many developed nations encountering the obesity epidemic. These include high sugar-sweetened beverage consumption, lower vegetable intake and greater consumption of foods prepared outside the home including fast foods. Each of these dietary behaviours may place young adults at increased risk for overweight and obesity. Evidence suggests many young adults with unhealthy nutrition behaviours are not considering nor preparing to make changes. To improve their nutrition and health as they progress through the lifecycle requires approaches specifically targeted to this age group. Strategies and programs should include both individual level and population approaches. The evidence base for prevention of weight gain and halting overweight and obesity in young adulthood is currently small with few studies of high quality. Studies modifying food environments in colleges and universities are also of limited quality, but sufficiently promising to conduct further research employing better, more sophisticated, study designs and additionally to include health outcome measures. More research into programs tailored to the needs of young adults is warranted with several studies already underway.

Comparison of fruit and vegetable intakes during weight loss in males and females

BACKGROUND/OBJECTIVES

Globally, fruit and vegetable intakes are well below recommendations despite ample evidence to link insufficient intake with increased risk of overweight and obesity. Intakes of fruits and vegetables in the general population differ between males and females, and although there is growing evidence of intakes in men and women during weight loss, evidence that directly compares intakes in men and women during weight loss is lacking. This study aimed to identify any differences between males and females in fruit and vegetable intakes and plasma carotenoid concentrations during weight loss, and determine whether there is a relationship between any changes in fruit and vegetable intakes and weight change in both males and females.

SUBJECTS/METHODS

Men and women (n=100; body mass index 25-40 kg/m(2)) aged 18-60 years were selected for the study. Dietary intake of fruits and vegetables was assessed using the Australian Eating Survey and fasting blood was collected to assess plasma carotenoids, which were determined by high-performance liquid chromatography.

RESULTS

There was little change in fruit or vegetable intakes during weight loss, although men tended to increase fruit intakes. Changes in intakes were influenced by baseline intakes, with males and females with the highest intakes at baseline reducing intakes. Males had better correlations between fruit and vegetable intakes and plasma carotenoid concentrations than females, and fruit and vegetable intakes during weight loss appear to predict weight loss for males but not females.

CONCLUSIONS

Fruit and vegetable intake during weight loss does not appear to differ largely between males and females.

Weighing the Evidence of Common Beliefs in Obesity Research

Obesity is a topic on which many views are strongly held in the absence of scientific evidence to support those views, and some views are strongly held despite evidence to contradict those views. We refer to the former as "presumptions" and the latter as "myths." Here, we present nine myths and 10 presumptions surrounding the effects of rapid weight loss; setting realistic goals in weight loss therapy; stage of change or readiness to lose weight; physical education classes; breastfeeding; daily self-weighing; genetic contribution to obesity; the "Freshman 15"; food deserts; regularly eating (versus skipping) breakfast; eating close to bedtime; eating more fruits and vegetables; weight cycling (i.e., yo-yo dieting); snacking; built environment; reducing screen time in childhood obesity; portion size; participation in family mealtime; and drinking water as a means of weight loss. For each of these, we describe the belief and present evidence that the belief is widely held or stated, reasons to support the conjecture that the belief might be true, evidence to directly support or refute the belief, and findings from randomized controlled trials, if available. We conclude with a discussion of the implications of these determinations, conjecture on why so many myths and presumptions exist, and suggestions for limiting the spread of these and other unsubstantiated beliefs about the obesity domain.

Weight loss effects from vegetable intake: a 12-month randomised controlled trial

Background/Objectives:

Direct evidence for the effects of vegetable intake on weight loss is qualified. The study aimed to assess the effect of higher vegetable consumption on weight loss.

Subjects/Methods:

A single blind parallel controlled trial was conducted with 120 overweight adults (mean body mass index=29.98 kg/m²) randomised to two energy deficit healthy diet advice groups differing only by doubling the serving (portion) sizes of vegetables in the comparator group. Data were analysed as intention-to-treat using a linear mixed model. Spearmans rho bivariate was used to explore relationships between percentage energy from vegetables and weight loss.

Results:

After 12 months, the study sample lost 6.5±5.2 kg (P<0.001 time) with no difference between groups (P>0.05 interaction). Both groups increased vegetable intake and lost weight in the first 3 months, and the change in weight was significantly correlated with higher proportions of energy consumed as vegetables (rho=–0.217, P=0.024). Fasting glucose, insulin and triglyceride levels decreased (P<0.001 time) and high-density lipoprotein cholesterol levels increased (P<0.001 time), with no difference between groups. Weight loss was sustained for 12 months by both groups, but the comparator group reported greater hunger satisfaction (P=0.005).

Conclusions:

Advice to consume a healthy low-energy diet leads to sustained weight loss, with reductions in cardiovascular disease risk factors regardless of an emphasis on more vegetables. In the short term, consuming a higher proportion of the dietary energy as vegetables may support a greater weight loss and the dietary pattern appears sustainable.