Peter M Clifton

Disclosures

Nat Clin Pract Gastroenterol Hepatol. 2008;5(12):672-681. 

In This Article

Summary and Introduction

Summary

In patients with obesity, low-fat diets seem to result in a weight loss of 3–4 kg at 3 years, but long-term data are limited. Calorie-controlled diets seem to outperform low-fat diets with reported weight losses of 6–7 kg at 4 years, but, again, data are very limited; an initial very-low-calorie diet approach does not lead to greater weight loss than low-fat diets in the long term. Use of meal replacements can lead to an 8 kg weight loss at 4 years, but this finding has been reported only in one, uncontrolled study. High-protein, low-carbohydrate (or very-low-carbohydrate) diets have also been evaluated and seem to be superior to high-carbohydrate diets at least for up to 2 years. Very-low-carbohydrate diets can lead to elevations in LDL cholesterol levels in some individuals. Cognitive behavioral therapy added to diet therapy can facilitate approximately 5 kg additional weight loss, and exercise can facilitate an additional 1–1.5 kg weight loss. Drug treatment, particularly with sibutramine and rimonabant, can increase weight loss with a mildly hypocaloric diet by an additional 3–5 kg, but weight-loss drugs are costly and have adverse effects. If dietary and medical therapies fail, gastric banding can lead to a weight loss of ~14% at 10 years, with greater losses of up to 25% with gastric bypass and gastroplasty. Bariatric surgery can also lead to a reduction in mortality and comorbidities but adverse effects can occur including nutritional deficiencies and gastrointestinal symptoms.

Introduction

Weight loss is important for reducing the risk of type 2 diabetes in individuals with obesity and impaired glucose homeostasis as well as improving dyslipidemia and reducing blood pressure.[1] Neither a large amount of weight loss nor weight normalization are required to achieve these effects.[2] Most dietary weight-loss strategies lead to reasonable weight loss at 6 months (i.e. loss of 8–10% of initial body weight), but the real challenge of treatment for obesity is long-term weight maintenance. Obese patients have an unrealistic view of the amount of weight that they can lose and this belief can have a dramatic impact on dietary intervention drop-out rates.[3] There are little data on weight maintenance beyond 12 months for most dietary treatment strategies. However, any study with a follow-up period of ≥6 months can be considered a weight maintenance study, as weight loss stabilizes between 3 and 6 months.[4] In this Review, short-term data on weight maintenance are discussed when 12-month data are not available, which is particularly the case for carbohydrate-restricted diets.

Serious caveats apply to all data discussed in this Review. Firstly, participants in trials of dietary therapy for obesity usually achieve better results than nontrial participants as they are more motivated and are offered greater supervision, therefore, results in clinical practice will inevitably be less favorable and more variable than those in a trial setting.[1] Secondly, high drop-out rates are observed in all studies of dietary therapies for obesity so intention-to-treat data are discussed when available.[2] Thirdly, there is often a 10-fold variation in weight-loss results achieved in any trial, ranging from weight gain to weight loss of over 20 kg for ostensibly the same intervention; most of this variation is related to patient compliance.[3] Fourthly, data on dietary therapy for obesity are almost universally obtained from white populations.[5] Finally, patients are invariably disappointed by the poor results of dietary treatment for obesity; however, a 5% weight loss maintained over the long term can have beneficial effects on levels of lipids and glucose.[6]

Dietary strategies for the treatment of obesity can be broadly divided into five types. Low-fat diets are focused primarily on limiting fat intake with no recommendations concerning caloric intake. Low-calorie diets reduce the amounts of all macronutrients, including fat, to achieve a daily caloric intake of 4.2–6.2 MJ. Low-calorie diets include meal-replacement diets. Very-low-calorie diets recommend a daily caloric intake of <4.2 MJ and invariably restrict fat and carbohydrate, but near normal protein intake is maintained. Carbohydrate-restricted diets specify either a modest restriction of carbohydrate and an increase in protein intake (e.g. the Zone diet or CSIRO diet) or a severe restriction of carbohydrate intake and an increase in protein and fat intake (e.g. the Atkins diet or South Beach diet). Low-glycemic-index diets mostly recommend a diet with a low glycemic load: carbohydrate intake is maintained but the type of carbohydrate consumed is changed to deliver a lower glycemic load.

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