How justifiable is it to distort the energy profile of a diet to obtain benefits in body weight control?

Departamento de Nutrición
Facultad de Farmacia
Universidad Complutense
28040 Madrid
Spain

E-mail: rortega{at}farm.ucm.es

Dear Sir:

We read with great interest the excellent article by Luscombe-Marsh et al (1). Without doubt, this study provides valuable information on the complex subject of weight control and the fight against obesity (2). However, the article raises some questions.

The authors study the progress of overweight and obese volunteers who received 1 of 2 isocaloric diets that differed in their protein and fat contents: 27 subjects received a low-fat, high-protein diet (29 ± 1% fat, 34 ± 0.8% protein), and 30 received a high-fat, standard-protein diet (45 ± 0.6% fat, 18 ± 0.3% protein), both over a 12-wk period of energy restriction and a 4-wk period of energy balance. The magnitude of weight loss and the improvements in insulin resistance and cardiovascular disease risk did not differ significantly between the 2 diets, and neither diet had any detrimental effects on bone turnover or renal function (1).

Our first concern is that the diets followed appear to differ too widely from the theoretical ideal (2, 3). There is general agreement that <30% of energy should come from fat, that 10-15% should come from protein, and that the remainder should be supplied by carbohydrates (2, 3). It would only be justified to diverge from this standard if weight control benefits could not be achieved by any more reasonable method. If overweight and obese persons can only lose weight by following such a drastic diet—and bearing in mind that a high percentage of the population (4) is currently trying to lose weight—then current nutritional aims for the populations of developed countries need to be modified. Perhaps the percentage of energy from carbohydrates should be reduced and fat and protein intakes increased?

A second concern is that if the usual reference values are taken into account (2, 3), the low-fat diet (29 ± 1% fat) to which the authors refer is actually one with an adequate amount of fat, whereas the standard-protein diet is somewhat high in proteins (18 ± 0.3% protein). Nevertheless, both diets provide just 37% of energy from carbohydrates. It is common in developed countries to see energy imbalances in the diet, with excessive intakes of protein and fat and only a small energy contribution from carbohydrates. It has even been shown that this imbalance is greater in overweight and obese individuals (5, 6). Given this background, the imposition of a further imbalance in the energy distribution of the diet would not appear to be the best form of weight control (7).

Some studies report that low-fat diets appear to be effective in the maintenance of weight control (7). Even in the absence of energy restriction, this type of diet can lead to weight losses of 5-10 kg in obese persons (8). Nonetheless, high-protein diets remain popular, which suggests that people perceive some type of benefit in them. One such benefit may be the increased feeling of satiety provided by dietary protein, which makes it easier to adhere to a reduced-energy diet and contributes to spontaneous reductions in energy intake (9). However, the role of protein in the regulation of long-term food intake and body weight is less clear (9). A major criticism of low-carbohydrate, high-protein, high-fat diets is that they may have adverse effects on health (9).

It is likely that many kinds of dietary modification can lead to weight loss, perhaps the most aberrant achieving the greatest losses. But it is important is to find out which can be successfully and healthily followed over the long term. The article by Luscombe-Marsh et al provides valuable information, but we question why a diet similar to a balanced diet in energy terms is ruled out in the control of body weight.

ACKNOWLEDGMENTS

The authors had no conflicts of interest to report.

REFERENCES

1. Luscombe-Marsh ND, Noakes M, Wittert GA, Keogh JB, Foster P, Clifton PM. Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids. Am J Clin Nutr 2005;81:762-72.
2. World Health Organization. Diet, nutrition and the prevention of chronic diseases. Report of a Joint WHO/FAO Expert Consultation. World Health Organ Tech Rep Ser 2003;916.
3. Ortega RM, López-Sobaler AM, Requejo AM, Andrés P. Nutritional objectives for the Spanish population. Recommended steps for improving the health of the population. In: Department of Nutrition, ed. Food composition. A basic tool for assessing nutritional status. Madrid, Spain: Complutense, 2004:86.
4. Ortega RM, Requejo AM, Quintas ME, Redondo MR, López-Sobaler AM, Andrés P. Concern regarding bodyweight and energy balance in a group of female university students from Madrid: differences with respect to body mass index. J Am Coll Nutr 1997;16:244-51.
5. Ortega RM, Redondo MR, Zamora MJ, López-Sobaler AM, Andrés P, Encinas-Sotillos A. Energy balance and caloric profile in the elderly obese or in those with overweight compared to those of normal weight. Med Clin (Barc) 1995;104:526-9.
6. Ortega RM, Requejo AM, Andrés P, López-Sobaler A, Redondo MR, González-Fernández M. Relationship between diet composition and body mass index in a group of Spanish adolescents. Br J Nutr 1995;74:765-73.
7. Ortega RM, Andrés P. Carbohydrates and obesity. Med Clin (Barc) 1998;110:797-801.
8. Astrup A, Toubro S, Raben A, Skov AR. The role of low-fat diets and fat substitutes in body weight management: what have we learned from clinical studies? J Am Diet Assoc 1997;97:S82-7.
9. Anderson GH, Moore SE. Dietary proteins in the regulation of food intake and body weight in humans. J Nutr 2004;134:S974-9.