Low Carbohydrate Diets: No Energy Restriction Required

The general consensus amongst mainstream medicine is that weight loss is only possible through forced energy restriction. The proponents of such diets also sometimes suggest the use of forced physical activity to further increase the energy deficit. However, even in the clinical setting, the data from forced energy restrictive trials does not show long-term benefits, and the high failure rates of such diets suggests that they are not effective. Studies from the nutritional sciences have suggested that forced energy restriction is not necessary to cause weight loss. Instead improvements in diet quality, particularly the avoidance of refined carbohydrates, have been investigated experimentally and found to cause weight loss in over weight individuals. The Mediterranean diet has shown benefits in this regard, perhaps due to its ability to reverse the insulin resistance associated with abdominal weight gain and obesity.

The Mediterranean diet is low in refined carbohydrates and contains high amounts of fibre and whole grains. This lowers the glycaemic index of the diet considerably when compared to a typical Western diet, and may control insulin release and reverse dysfunction in the insulin receptor. If lowering insulin release is beneficial to the process of weight loss, this would explain the benefit of low carbohydrate diets reported both in the scientific literature and anecdotally. In addition, low carbohydrate diets also force a limitation on the sort of refined carbohydrate that typify by the Western diet, and are now implicated as a possible cause of obesity. However, despite accumulating evidence showing the benefits of both the Mediterranean and low carbohydrate diet, modern medicine continues with its fixation of the low fat low cholesterol diet, which in comparison performs poorly. As has been demonstrated in direct comparisons of the diets.

For example, researchers1 have investigated the effects a low fat diet, a low carbohydrate diet, or a Mediterranean diet, in 322 moderately obese subjects. The low fat diet was based on the recommendation of the American Heart Association, with 30 % of calories from fat, and an intake of ≤ 300 mg cholesterol. The Mediterranean diet was based on the traditional version of the diet, with high intakes of vegetables and fruit, low intakes of animal fat, and protein from fish and poultry. The Mediterranean diet limited fat to 35 % of calories mainly from olive oil and nuts. Both the low fat and Mediterranean diet groups were restricted to 1800 or 1500 kcal per day for men and women, respectively. The low carbohydrate diet group was restricted to 20 grams carbohydrate per day for 2 months, then 120 grams per day thereafter, but could eat unlimited amounts of protein and fat.

Daily energy intake went down in all groups as reported by dietary questionnaire at 6, 12 and 24 months. This argues against the benefits of forced energy restriction, as it is clear from these results that allowing ad libitum access to low carbohydrates foods causes energy restriction, albeit unforced and regulated naturally by the body. This supports evidence that shows that high protein diets are able to cause weight loss because protein is the main regulator of appetite, due to its slowing of gastric emptying. Even more interesting was the fact that despite not being forced to restrict calories in any way, the low carbohydrate diet group lost significantly more weight that the other diet groups. At the 24 month time point, the weight loss was 3.3, 4.6 and 5.5 kg for the low fat, Mediterranean and low carbohydrate diets, respectively. Adiponectin concentrations increased in all groups.

High density lipoprotein (HDL) increased in all groups, probably as a result of weight loss, but the largest rise was seen in the low carbohydrate group. Triglycerides decrease significantly in the low carbohydrate group compared to the low fat group. While low density lipoprotein (LDL) did not change significantly in any group, the rise in HDL caused a favourable shift in the HDL to LDL ratio which would reduce cardiovascular risk. This is more evidence that dietary cholesterol is not the cause of cardiovascular disease. Despite being allowed access to high intakes of unrestricted saturated fat and cholesterol, the low carbohydrate group had the most beneficial changes in circulating plasma lipoprotein levels. Those consuming the diet recommended by the American Heart Association had the least improvement in their lipoprotein levels, which suggests the science underlying the diet is flawed.

Of the diabetic subjects in the study, only those in the Mediterranean diet group had a decrease in fasting plasma glucose levels, and this was significantly different to the low fat diet group, who showed an increase. This supports data from other studies that indicate the Mediterranean diet is able to reduce plasma glucose levels in those with blood sugar disorders. Most of the changes seen in this study likely relate directly to the weight loss seen in the subjects. Benefits to plasma lipoproteins for example are known to improve with weight loss irrespective of diet consumed. However, the Mediterranean diet produced benefits in fasting glucose levels and this may relate specifically to the components of the diet, rather than weight loss. Circulating plasma C-reactive protein (CRP) decreased in both the low carbohydrate group and the Mediterranean diet group, suggesting that inflammation had been reduced.

Overall these results question the validity of the forced energy restriction mantra.  The beneficial weight loss effects of the low carbohydrate diet shows that weight gain and obesity is far more complex than the forced energy proponents suppose. Based on this study it is difficult to find justification to recommend forced energy restriction for weight loss. Both the Mediterranean diet and the low carbohydrate diet showed benefits in particular areas, but the low fat diet performed more poorly in every respect. These results also highlight the absurdity of the cholesterol theory of heart disease, whereby dietary cholesterol is claimed to be the cause of cardiovascular disease. Those with free access to unlimited saturated fat and cholesterol containing foods showed the greatest improvement in plasma lipoprotein concentrations in terms of their risk for cardiovascular disease. This study supports growing evidence showing benefits to avoiding refined carbohydrates.


1Shai, I., Schwarzfuchs, D., Herkin, Y., Shahar, D., Witkow, S., Greenberg, I., Golan, R., Fraser, D., Bolotin, A., Vardi, H., Tangi-Rozental, O., Zuk-Ramot, R., Sarusi, B., Brickner, D., Schwartz, Z., Sheiner, E., Marko, R., Katorza, E., Thiery, J., Fiedler, G. M., Bluher, M., Sturnvoll, M. and Stamfer, M. J. 2008. Weight loss with a low-carbohydrate, Mediterranean or low-fat diet. The New England Journal of Medicine. 359(3): 229-241

About Robert Barrington

Robert Barrington is a writer, nutritionist, lecturer and philosopher.
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