Review: Diet in the management of weight loss.

Low-calorie diets can lower total body weight by an average of 8% in the short term. These diets are well-tolerated and characterize successful strategies in maintaining significant weight loss over a 5-year period. Very-low-calorie diets produce a more rapid weight loss but should only be used for fewer than 16 weeks because of clinical adverse effects. Diets that are severely restricted in carbohydrates (3%–10% of total energy intake) and do not emphasize a reduction of energy intake may be effective in reducing weight in the short term, but there is no evidence that they are sustainable or innocuous in the long term because their high saturated-fat content may be atherogenic. Fat restriction in a weight-loss regimen is beneficial, but the optimal percentage has yet to be determined.

Which diets result in safe weight loss, have positive long-term consequences for chronic disease risk factors, and are sustainable in the long term? This question has been only partially answered. Comparing dietary trials is difficult for several reasons: diet compositions vary in the amount and type of carbohydrates and fats, amount of protein, and degree that energy intake is restricted, all of which have intricate bearings on weight regulation; diets have specific actions on appetite and food preference that affect drop-out rates; study populations may have different associated diseases that modify outcomes; and the choice of statistical analyses can bias results.

The National Institutes of Health reviewed 34 randomized controlled trials to assess the effectiveness of low-calorie diets for lowering body weight, decreasing abdominal fat and improving cardiorespiratory fitness.8 The review concluded that low-calorie diets can lower total body weight by an average of about 8% during a period of 3–12 months (evidence category A). Weight-loss and weight-loss maintenance interventions lasting 3–4.5 years (4 studies only) resulted in an average weight loss of 4%, well below the definition proposed for successful weight loss (a decrease in 10% of body weight sustained for more than 1 year).7 Low-calorie diets resulting in weight loss also lower the amount of abdominal fat, as shown by a reduction in waist circumference of 1.5–9.5 cm (evidence category A). The National Institutes of Health review also concluded that low-calorie diets alone do not improve cardiorespiratory fitness as measured by maximum rate of oxygen consumption (evidence category B),8 which reinforces the importance of combining diet and exercise programs in weight-loss interventions. Behaviour therapy in conjunction with dietary interventions (including low-calorie diets) has been shown to result in additional weight loss in the short term (1 year) but not in the long term (3–5 years) (evidence category B).

There is a debate regarding the effectiveness of low-fat diets in weight reduction.23–28 Astrup and colleagues26 conducted a meta-analysis of 16 trials of 2–12 months' duration, of which 14 were randomized. They reported that low-fat diets without intentional restriction of energy intake resulted in greater weight loss (3.2 kg, 95% confidence interval 1.9–4.5 kg, p < 0.001) than did habitual, or medium-fat, diets ad libitum. ... The National Institutes of Health review also concluded that lower-fat diets (20%–30% of total energy intake) contribute to lower energy intake; there is little evidence that low-fat diets with no reduction in energy intake result in weight loss.

We still have no definitive answer as to which diets sustain long-term weight loss. The National Weight Control Registry in the United States provides useful information regarding successful weight-loss maintenance strategies.81 This registry includes people who have lost more than 13 kg of body weight and successfully maintained that weight loss for over 5 years. Over 4000 people are in the registry. The dietary pattern generally shared among participants included low amounts of fat (about 24% of the total daily energy intake), high amounts of carbohydrate, and a low energy intake (5460–6300 kJ/d). Most eat breakfast daily, self-monitor weight and are physically active. Other studies report similar strategies for successful weight-loss maintenance, such as monitoring food portion sizes, energy and fat intake, and body weight, and avoiding the use of food to regulate mood.

Overall, low-calorie diets are a safe strategy for weight loss. A sample 5040-kJ diet plan based on Canada's Food Guide to Healthy Eating is outlined in the online appendix (available at www.cmaj.ca/cgi/content/full/174/1/56/DC1). A sedentary woman 45 years of age with a body mass index of 31 kg/m2 (height 167.6 cm [5'6"], weight 87.5 kg [192.5 pounds]) and an energy requirement of 7988 kJ per day (calculated using the Harris–Benedict equation) can achieve a body mass index of about 26 kg/m2 after 6 months on a 5040-kJ/d low-calorie diet. ... Low-carbohydrate diets and diets high in saturated fat are not recommended.

Successful Weight Loss Among Obese U.S. Adults

Purpose: To identify strategies associated with losing at least 5% and 10% of body weight.

Sciamanna and colleagues identifıed 14 strategies reported to be successful for 10% weight loss among a national mail panel survey, reporting the strongest associations for weight loss programs, eating fruits and vegetables, eating healthy snacks, limiting carbohydrates, controlling portions, doing different kinds of exercises, and focusing on the progress they had made. Among members of the National Weight Control Registry, the most common strategies associated with success included restricting types of foods, limiting quantity of food, and counting calories.

Results: Of 4021 obese adults, 2523 (63%) reported trying to lose weight in the previous year. Among those attempting weight loss, 1026 (40%) lost ?5% and 510 (20%)lost ?10% weight. After adjustment for potential confounders, strategies associated with losing 5% weight included eating less fat ; exercising more; and using prescription weight loss medications. Eating less fat; exercising more; and using prescription weight loss medications were also associated with losing 10% weight, as was joining commercial weight loss programs. Adults eating diet products were less likely to achieve 10% weight loss. Liquid diets, nonprescription diet pills, and popular diets had no association with successful weight loss.

The present study has several limitations. Because this is a cross-sectional observational study based mostly on self-reported information, results suggest associations and do not signify causality.Although there is likely reporting bias for body weight,this study demonstrates a high correlation between self-reported current body weight and measured body weight.

Energetics of obesity and weight control: does diet composition matter?

Diet in the management of weight loss

Successful Weight Loss Among Obese U.S. Adults