Dietary Treatment for Obesity- Which is the Best Diet?

A review article in the New England Journal of Medicine May1,2008 examines non-sugical treatment of obesity. The merits of low calorie, low fat, low carbohydrate  and high protein diets were discussed. The following dietary strategies were discussed:

·        Calorie restriction. To lose weight, energy intake must be less than energy expenditure. Reduced-calorie diets include those with very low (less than 800 kcal daily), low (800 to 1500 kcal daily), and moderate (about 500 kcal less than typical daily intake) calorie intake. In the absence of changes in physical activity, intake of about 500 fewer kcal per day predicts a weight loss of about .5 kg per week. Very-low-calorie diets should be used only when more rapid weight loss is needed, and medical monitoring is necessary with such diets.¹³

·        Low carbohydrate (diets less than 60 g of carbohydrates daily). Studies have shown that in the first 6 months, low-carbohydrate diets result in significantly more weight loss than low-fat diets^2,3 with the exception of one study,⁴ unfortunately this difference was no longer significant at 12 months. Diets low in carbohydrates (as compared with those low in fat) result in lower blood sugar levels in patients with elevated blood sugar levels, lower fasting levels of plasma triglycerides, and higher levels of HDL cholesterol(good cholesterol); but, they also tend to increase LDL cholesterol levels.

·        Low fat diets ^. Lower fat intake has been associated with lower (or at least not greater) body weight,⁵ low-fat diets remain controversial.⁶ The traditional approach to weight reduction has been to restrict dietary fats to less than 30% of total calories. A very-low-fat diet typically has no more than 15% of total calories from fat, with about 15% of calories from protein and about 70% from carbohydrates. The Lifestyle Heart Trial, an intensive program of dietary counseling, stress management, and moderate exercise in patients with coronary heart disease, which reduced subjects' fat intake to 7% of calories, resulted in a weight loss of about 11 kg after 1 year, with a lower rate of progression of coronary heart disease at 5 years.⁷ However, very-low-fat diets are difficult to maintain in the long-term basis.

·        High protein diets. Diets high in protein are usually also high in fat. Because protein may enhance satiety, increase meal-induced heat generation, protect lean body mass, and decrease energy efficiency,⁸ the substitution of protein for carbohydrates during weight loss has been increasingly emphasized. In randomized trials, substitution of protein for carbohydrates in calorie-restricted diets resulted in more weight loss.^9,10

·        Low Glycaemic Index Diets(Low GI diets)The glycemic index is a rating system for foods based on how much they raise blood glucose levels 2 hours after their consumption. Studies show reduced-glycemic-index diets have not resulted in increased weight loss beyond that explained by caloric restriction.^11,12  

Summarising the evidence, the most effective dietary weight loss strategy is a low calorie diet which is high in protein and low in carbohydrates and fats.  For those who have difficulty adhering to dietary change, medication and supplements to reduce appetite can be added.  These will be discussed in a separate article.

REFERENCES

1. Eckel,R H Nonsurgical Management of Obesity in Adults New England Journal of Medicine 2008 Vol358:1941-1950

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2.  Willett WC. Dietary fat plays a major role in obesity: no. Obes Rev 2002;3:59-68. [CrossRef][Medline]
3. Ornish D, Brown SE, Scherwitz LW, et al. Can lifestyle changes reverse coronary heart disease? The Lifestyle Heart Trial. Lancet 1990;336:129-133
4. Westerterp-Plantenga MS, Lejeune MP. Protein intake and body-weight regulation. Appetite 2005;45:187-190. [CrossRef][ISI][Medline]
5. Noakes M, Keogh JB, Foster PR, Clifton PM. Effect of an energy-restricted, high-protein, low-fat diet relative to a conventional high-carbohydrate, low-fat diet on weight loss, body composition, nutritional status, and markers of cardiovascular health in obese women. Am J Clin Nutr 2005;81:1298-1306. [Free Full Text]
6. Due A, Toubro S, Skov AR, Astrup A. Effect of normal-fat diets, either medium or high in protein, on body weight in overweight subjects: a randomised 1-year trial. Int J Obes Relat Metab Disord 2004;28:1283-1290.

1. Ebbeling CB, Leidig MM, Feldman HA, Lovesky MM, Ludwig DS. Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial. JAMA 2007;297:2092-2102. [Erratum, JAMA 2007;298:627.] [Free Full Text