W. Douthwaite

Effect of reducing total fat intake on body weight: systematic review and meta-analysis of randomised controlled trials and cohort studies

Objective To investigate the relation between total fat intake and body weight in adults and children. Design Systematic review and meta-analysis of randomised controlled trials and cohort studies. Data sources Medline, Embase, CINAHL, and the Cochrane Central Register of Controlled Trials to June 2010. Inclusion criteria Randomised controlled trials and cohort studies of adults or children that compared lower versus usual total fat intake and assessed the effects on measures of body fatness (body weight, body mass index, or waist circumference) after at least six months (randomised controlled trials) or one year (in cohorts). Randomised controlled trials with any intention to reduce weight in participants or confounded by additional medical or lifestyle interventions were excluded. Data extraction Data were extracted and validity was assessed independently and in duplicate. Random effects meta-analyses, subgroups, sensitivity analyses, and metaregression were done. Results 33 randomised controlled trials (73 589 participants) and 10 cohort studies were included, all from developed countries. Meta-analysis of data from the trials suggested that diets lower in total fat were associated with lower relative body weight (by 1.6 kg, 95% confidence interval −2.0 to −1.2 kg, I2=75%, 57 735 participants). Lower weight gain in the low fat arm compared with the control arm was consistent across trials, but the size of the effect varied. Metaregression suggested that greater reduction in total fat intake and lower baseline fat intake were associated with greater relative weight loss, explaining most of the heterogeneity. The significant effect of a low fat diet on weight was not lost in sensitivity analyses (including removing trials that expended greater time and attention on low fat groups). Lower total fat intake also led to lower body mass index (−0.51 kg/m2, 95% confidence interval −0.76 to −0.26, nine trials, I2=77%) and waist circumference (by 0.3 cm, 95% confidence interval −0.58 to −0.02, 15 671 women, one trial). There was no suggestion of negative effects on other cardiovascular risk factors (lipid levels or blood pressure). GRADE assessment suggested high quality evidence for the relation between total fat intake and body weight in adults. Only one randomised controlled trial and three cohort studies were found in children and young people, but these confirmed a positive relation between total fat intake and weight gain. Conclusions There is high quality, consistent evidence that reduction of total fat intake has been achieved in large numbers of both healthy and at risk trial participants over many years. Lower total fat intake leads to small but statistically significant and clinically meaningful, sustained reductions in body weight in adults in studies with baseline fat intakes of 28-43% of energy intake and durations from six months to over eight years. Evidence supports a similar effect in children and young people.

The association between diet and physical activity and subsequent excess weight gain and obesity assessed at 5 years of age or older: a systematic review of the epidemiological evidence

Background The geographical or natural conditions of a country affect the manner in which economic growth takes place. Overcoming natural impediments and making use of geographical and natural advantages is the duty of economic experts and researchers. In order to overcome geographical and natural hardships, investments above international norm are needed and, on the contrary, by the optimal use of natural and regional advantages of a given area, less investment is needed for economic growth. In spite of all defeats and victories, ups and downs, the inhabitants of this land have relatively always played a determining role in West Asia and have greatly influenced and being influenced by the neighboring events and nation. The Iranian territory is located inside the desert belt of the Northern Hemisphere and is geographically placed in a belt line, the same as the plains in North Africa, Tibet and Turkistan. The country of Iran is about 1648195 square kilometers. From the total 1648195 square kilometers of the Country nearly 509442 square kilometers are used in agriculture and the rest is uncultivable areas or covered by cities, villages, lakes and roads. From 31% cultivable land in Iran; the two Northern provinces on the Caspian Sea coasts with an area of 5.5% of the overall area of Iran form more than 20% of the cultivable lands. 11 Introduction Obesity arises from a complex interplay between genetic susceptibility and behaviour, primarily relating to dietary habits and physical activity (Foresight, 2007). Evidence for specific behavioural factors that promote or protect against excess weight gain have been usefully reviewed (Wareham, 2007); (Jebb, 2007), and is more limited in children compared with adults (Rennie et al., 2005). A number of behavioural risk factors have been postulated, including TV viewing, diets with a high energy density, and fast foods. Most evidence is derived from cross sectional studies which can frequently produce conflicting results. Prospective studies with accurate measure of diet and physical activity exposures, and outcomes in terms of body fatness, are deemed to provide the more robust evidence on which to base interventions to achieve long-term behavioural change and prevent excess weight gain. The question to be answered by this comprehensive systematic review of the epidemiological evidence was ‘What is the association between food, food groups, nutrition and physical activity and subsequent excess weight gain and obesity in humans?’ Relevant exposures include patterns of diet; breastfeeding; food and drink; food preparation; dietary constituents; physical activity and inactivity; energy intake; energy density of diet; energy expenditure. Outcomes in adulthood and childhood have reported separately. Outcomes of interest included markers of weight gain; overweight; obesity; markers of body composition; markers of distribution of fat. The results of this review will provide evidence of association, but not causes, of subsequent excess weight gain and obesity. There is a degree of uncertainty inherent in epidemiological evidence, given that it is impossible to determine if there are uncontrolled variables, including genetic variations. The well known association between relatively high non caloric sweetner usage and subsequent weight gain is a useful reminder that, whilst an evidence based approach is critical to the process of scientific enquiry, consideration of evidence from other types of studies (mechanistic studies, intervention studies) and understanding the context of the evidence reviewed is essential if we are to provide policy makers, industry, service providers and the public with sensible recommendations.

Evidence-based recommendations for the development of obesity prevention programs targeted at preschool children

The ToyBox intervention was developed using an evidence‐based approach, using the findings of four reviews. These reviews included three critical and narrative reviews of educational strategies and psychological approaches explaining young childrens acquisition and formation of energy‐balance related behaviours, and the management of these behaviours, and also a systematic review of behavioural models underpinning school‐based interventions in preschool and school settings for the prevention of obesity in children aged 4–6 years.

A narrative review of psychological and educational strategies applied to young children's eating behaviours aimed at reducing obesity risk

Strategies to reduce risk of obesity by influencing preschool childrens eating behaviour are reviewed. The studies are placed in the context of relevant psychological processes, including inherited and acquired preferences, and behavioural traits, such as food neophobia, ‘enjoyment of food’ and ‘satiety responsiveness’. These are important influences on how children respond to feeding practices, as well as predictors of obesity risk. Nevertheless, in young children, food environment and experience are especially important for establishing eating habits and food preferences. Providing information to parents, or to children, on healthy feeding is insufficient. Acceptance of healthy foods can be encouraged by five to ten repeated tastes. Recent evidence suggests rewarding healthy eating can be successful, even for verbal praise alone, but that palatable foods should not be used as rewards for eating. Intake of healthier foods can be promoted by increasing portion size, especially in the beginning of the meal. Parental strategies of pressuring to eat and restriction do not appear to be causally linked to obesity, but are instead primarily responses to childrens eating tendencies and weight. Moderate rather than frequent restriction may improve healthy eating in children. Actively positive social modelling by adults and peers can be effective in encouraging healthier eating.

Critical narrative review to identify educational strategies promoting physical activity in preschool

The aim of this narrative review is critically to evaluate educational strategies promoting physical activity that are used in the preschool setting in the context of obesity prevention programmes. Literature search was conducted between April and August 2010 in English and German databases (PubMED, PsychINFO, PSYNDEX, ERIC, FIS Bildung). Outcomes considered were time and intensity of physical activity, motor skills or measures of body composition. A total of 19 studies were included. Ten studies added physical activity lessons into their curriculum, one study provided more time for free play, eight studies focused on the social and play environment. Studies reporting positive outcomes implemented physical activity sessions that lasted at least 30 min d−1. Several studies showed that children are most active in the first 10–15 min. The existence or installation of playground markings or fixed play equipment had no effect, whereas the presence or addition of portable play equipment was positively correlated with moderate‐to‐vigorous physical activity. Teacher training may be a key element for successful interventions. To overcome time constraints, a suggested solution is to integrate physical activity into daily routines and other areas of the preschool curriculum.