The Best Evidence for Calorie-Based Weight Loss

Calorie-based weight loss studies focus on reducing the number of calories consumed and/or increasing the number of calories burned to create a calorie deficit, leading to weight loss. Here is a summary of some key findings from calorie-based weight loss studies:

1. A study published in the New England Journal of Medicine found that reducing calorie intake by 500-750 calories per day resulted in an average weight loss of 4-7 kg over a six-month period. Participants who combined calorie reduction with increased physical activity had even greater weight loss (1). That's 9 to 15 lbs lost in six months, little more than could be explained by water weight fluctuations in the course of a few weeks.
2. Another study published in the Journal of the American Medical Association found that a low-fat, reduced-calorie diet was effective in achieving weight loss in overweight and obese individuals. The study found that after two years, participants on the low-fat diet had an average weight loss of 3.2 kg (2). After two years, participants lost an average of 7lbs, the equivalent to a few weeks of targeted weight loss.
3. A review of multiple studies published in the Journal of the Academy of Nutrition and Dietetics found that calorie restriction is effective for weight loss, and that adherence to a reduced-calorie diet is the most important factor for success (3). This is a circular observation. "People who eat less get smaller; therefore, to get smaller, you have to keep eating less."
4. A study published in the International Journal of Obesity found that reducing calorie intake by 500-750 calories per day was effective in reducing body weight and fat mass in overweight and obese individuals (4). We have now seen how these organizations define "effective" as a few pounds lost over the course of years.
5. Another study published in the American Journal of Clinical Nutrition found that reducing calorie intake by 500-750 calories per day was effective in reducing body weight and improving cardiovascular risk factors in overweight and obese individuals (5). Again, this is a circular description of "what" and not an explanation of "how." 

Overall, calorie-based weight loss studies consistently demonstrate that strictly focusing on the reduction of calories yields very minor results and almost none in the long-term. These are among the strongest pieces of evidence in favor of calories as the standalone paradigm for weight loss. Clearly, more considerations than mere calories must be made in order to successfully lose significant weight and keep it off.

References:

1. Sacks FM, et al. Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates. N Engl J Med. 2009 Feb 26;360(9):859-73.
2. Dansinger ML, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets for Weight Loss and Heart Disease Risk Reduction. JAMA. 2005 Jan 5;293(1):43-53.
3. Gardner CD, et al. Weight Loss and Adherence in a Commercial Weight Loss Program: A Randomized Trial of Calorie Restriction versus Calorie Restriction plus Exercise. J Acad Nutr Diet. 2012 Aug;112(8):1335-42.
4. Gardner CD, et al. Effect of Reduced Dietary Intake on Energy Expenditure, Protein Turnover, and Glucose Metabolism in Nonobese Adults. Int J Obes Relat Metab Disord. 2003 Jul;27(7):930-6.
5. McManus K, et al. A Randomized Controlled Trial of a Moderate-Fat, Low-Energy Diet Compared with a Low Fat, Low-Energy Diet for Weight Loss in Overweight Adults. Am J Clin Nutr. 2001 Jul;74(1): 21-8.

Bibliography:

• Sacks FM, et al. Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates. N Engl J Med. 2009 Feb 26;360(9):859-73.
• Dansinger ML, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets for Weight Loss and Heart Disease Risk Reduction. JAMA. 2005 Jan 5;293(1):43-53.
• Gardner CD, et al. Weight Loss and Adherence in a Commercial Weight Loss Program: A Randomized Trial of Calorie