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LETTER TO THE EDITOR |
Department of Human Nutrition
Centre for Advanced Food Studies
The Royal Veterinary and Agricultural University
Rolighedsvej 30
DK-1958 Frederiksberg
E-mail: ast{at}kvl.dks
Dear Sir:
Contaldo and Pasinisi raise important questions about whether increases in the protein content of the diet should be recommended for the prevention and treatment of obesity. In my editorial I mainly addressed the potential health benefits of increasing the proportion of dietary energy provided by protein at the expense of a reduction in fat and carbohydrate sources that are less satiating. I can only agree that many other issues need to be taken into account, such as safety aspects, economy, and environmental issues, before such recommendations should be made.
In no way do I wish to suggest that overweight and obesity are "protein-deficiency conditions," but increasing the proportion of protein in the diet may be one way to attenuate the obesity problem in a sedentary population and, thereby, to help reduce many of the obesity-associated comorbidities. Current evidence from experimental and intervention studies suggests that an increase in the amount of energy provided by protein from the current 15–18% in most diets to 20–35% is associated with a spontaneous reduction in total energy intake and a weight loss of relevance for obese and diabetic subjects (1-4).
Contaldo and Pasinisi note that many individuals already consume high amounts of protein. It is obviously correct that even if a diet providing only 10% of calories from protein is consumed, it is still possible to get high amounts of protein if the total amount of calories consumed is high. However, evidence suggests that it is not just the absolute amount of protein (grams per day) consumed that is important, but that a high proportion of energy (% of calories) from protein is what results in a reduction in total caloric intake (1). Consequently, a high-protein diet may actually reduce the total amount of protein eaten, which is a highly relevant issue to be addressed in light of safety and environmental corollaries. Using data from the study by Due et al (1), I will provide an example to support the supposition that a high-protein diet does not necessarily result in an increase in total protein intake. An average obese individual has an energy requirement of 2500 kcal/d, which is provided by a diet in which 18% of the calories (or 107 g) come from protein. During the first 3 mo that the subjects consumed a high-protein diet providing 25% of calories from protein, the fat loss was consistent with an energy deficit of 700 kcal/d. Because energy requirements due to the weight loss decreased by 
100 kcal/d, the energy intake would have been 1700 kcal/d, of which 25% of energy (or 101 g) was protein.
Most experimental studies suggest that the replacement of some carbohydrate with protein has a neutral or even positive influence on inflammation and on risk factors for type 2 diabetes, cardiovascular disease, and osteoporosis (2-7). The increased protein content of the diet will normally be based on shellfish, fish, poultry, game, lean pork and beef, low-fat dairy products, lentils, and beans. However, our knowledge about the health effects of lean meat and dairy products is still limited. Whereas low-fat dairy products may be beneficial for preventing obesity, the metabolic syndrome, type 2 diabetes (8), and cardiovascular disease, there is concern that this food group may play a role in certain cancers. Similarly, processed meat may increase the risk of type 2 diabetes (9). Even so, on the basis of the available evidence, I find it difficult to warn individuals who will benefit from weight loss against replacing some of the less-nutritious carbohydrate with protein.
However, there are many aspects of high-protein diets that need to be addressed. We are currently running a large dietary intervention study (DiOGenes: Diet, Obesity and Genes) to identify the diet that is most effective for protecting against weight gain and weight regain in a susceptible population of obese and overweight individuals and their overweight children (10). This 6–12-mo dietary intervention will investigate the effect of different dietary components (high and normal protein contents and high- and low-glycemic-index carbohydrates) on weight-loss maintenance in 350 families in 8 European research centers. In particular, the safety and tolerability of high-protein diets in children will be addressed. Such a study would not have been initiated unless there was a need for more evidence before a higher-protein diet can be more widely recommended for weight control.
ACKNOWLEDGMENTS
The author had no conflict of interest related to the topic of this letter.
REFERENCES
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