Evidence suggests that calorie restricted diets are not successful at causing long-term weight loss due to poor attrition and compliance rates. Rather, changing the quality of the diet without energy restriction, to incorporate higher intakes of fruits, vegetables, fibre, whole grains, antioxidants and essential fatty acids, shows more promise by allowing better long-tern adherence to the dietary changes. Changing to a high quality diets has been shown to result in weight loss, without the need to deliberately restrict calories, in a number of studies. Much research has been published on energy restricted diet, but the success of long-term trials is poor, with positive findings being restricted to those studies of a short duration. Because of this researchers1 have investigated the compliance of 322 moderately obese subjects (body mass index 31kg/m2) to dietary changes that involved switching to a Mediterranean diet, a low fat diet or low carbohydrate diet.
The evaluation of the dietary compliance was achieved by frequent food questionnaire. The low fat diet adhered to the American Heart Association guidelines (20-30% calories from fat, 7-10% calories from saturated fat, 200-300 mg cholesterol), the Mediterranean diet comprised of 40% of calories from fat, mainly olive oil and nuts, and the low carbohydrate diet (based on the Atkin’s diet) comprised of an initial 20g of carbohydrate for 2 months followed by 100g of carbohydrates thereafter. All diets restricted energy intake to 1200-1500 and 1500-1800kcals for women and men, respectively. The researchers encouraged vegetarian sources for the protein in the low carbohydrate diet. Successful dieters were defined by the researchers as those who lost 5% of their total body weight, which they claim represents the minimum threshold for physical benefits. Unsuccessful subjects were those who gained weight or failed to lose 5% of total body weight.
The initial mean weight loss was 3.3, 4.6 and 5.5kg, for the low fat, Mediterranean and low carbohydrate diet, respectively. These results suggest that only the low carbohydrate diet was successful, based on the researchers own criteria. This supports large volumes of research that show that calorie restriction is not effective for weight loss. In addition, there was no effort by the researchers to quantify the type of weight loss, and it was not reported whether the weight loss was body fat, skeletal tissue, glycogen, water or muscle. The low carbohydrate diet also caused a significantly greater reduction in circulating lipids compared to the Mediterranean and low fat diet. The overall attrition rate was 15.5% after 24 months. Attrition rates in the individual diets were 9.6, 14.7 and 22% in the low fat, Mediterranean and low carbohydrate diets respectively, with more attrition attributed to women and smokers.
As has been shown in previous studies, initial weight loss in subjects was predictive of adherence to the diet, suggesting that those who do not lose weight initially are more likely to deviate from the diet and are unlikely to make future weight reductions. Of the diets, those on the low carbohydrate diet were the most disappointed with their diet selection and had the highest attrition rate, yet these individuals lost the most weight and had the best improvements in blood chemistry. A low carbohydrate diet therefore appears to be the most effective of the three diets, if the diet can be adhered to long-term. Interestingly disappointment with the diets were not significantly different after 2 months, suggesting that perception of the low carbohydrate diet may have been biased prior to the study, perhaps by mainstream media and anecdotal evidence.
The recommendation by the researchers to favour vegetable protein in the low carbohydrate diet is strange, because the Atkin’s diet recommends protein sources to come from animal foods predominantly. This may have affected the results because vegetable foods are a poor source of high quality protein and care must be taken to correctly combine foods to ensure adequate essential amino acids. The researchers also overemphasised the use of olive oil in the Mediterranean diet, as this is usually used as an accompaniment to other foods. In addition, there was no emphasis that the oil should be unrefined virgin oil. Based on the fact that the researchers did not include the weight gain of subjects who dropped out, and that compliance with the diets was poor (only 57% at 24 months), these results add further evidence that calorie restriction does not lead to successful long-term weight loss.
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