A recent study published in the British Medical Journal has received an enormous amount of publicity. In a well-designed protocol, investigators studied the effect of a low carbohydrate diet on energy expenditure. Traditional thinking is a calorie is a calorie whether it comes from protein, fat or carbohydrate. The researchers found, however, that subjects consuming a low carbohydrate diet burned significantly more calories per day.
The objective of the study was to test the carbohydrate-insulin model of obesity. In this model high carbohydrate intake stimulates insulin release which results in greater fat storage leading to obesity. To test the hypothesis subjects, following a weight loss period in which they lost 12% of their body weight, the subjects were assigned to one of three diets for 20 weeks:
- 20% Carb, 20% Protein, 60% Fat
- 40% Carb, 20% Protein, 40% Fat
- 60% Carb, 20% Protein, 20% Fat
Subjects on the low carb diet burned on average 209 calories more per day than those on the high carb diet. According to the researchers this metabolic effect may improve the effectiveness of obesity treatment. However there are lots of cautions with this study.
The study subjects had their meals prepared, individual energy measurements were made repeatedly and there was intense monitoring of the subjects by the research team. In other words this was not an approach for someone trying to lose weight. Even the investigators concluded the protocol was too costly and complicated to be practical. Also there are some other issues that could have influenced the results. For example, the low carb subjects consumed a high fat diet. Fat stimulates the release of satiety proteins which affects food consumption. There also could be issues with patient compliance.
In spite of these limitations the study results are extremely provocative and provide additional insight on whether macro-nutrients are metabolized differently. This should not be a surprise to endurance athletes and in next week's tip, I'll review the implications of this study on endurance performance.