Pilot 12-Week Weight-Loss Comparison: Low-Fat versus Low-Carbohydrate (Ketogenic) Diets

The following summarizes information presented at multiple conferences on a pilot study conducted by Greene et al. This information was written by Atkins professionals.

Obesity Research

Greene, P., Willett, W., Devecis, J., et al., “Pilot 12-Week Feeding Weight-Loss Comparison: Low-Fat vs Low-Carbohydrate (Ketogenic) Diets,” Abstract Presented at The North American Association for the Study of Obesity Annual Meeting 2003, Obesity Research, 11S, 2003, page 95OR.

Greene, P.J., Devecis, J., Willett, W.C., “Effects of Low-Fat Vs Ultra-Low-Carbohydrate Weight-Loss Diets: A 12-Week Pilot Feeding Study,” abstract presented at Nutrition Week 2004, February 9-12, 2004, in Las Vegas, Nevada.



Some researchers claim that people only lose weight on very low carb diets due to a reduction in calorie intake. Others have argued that very low carb diets offer a “metabolic advantage” allowing people to lose weight without restricting calories. The objective of this study was to evaluate if people who follow very low carb diets lose weight only due to restricting calories.


Twenty-one participants were recruited and were randomly assigned to three separate diets for 12 weeks: a low fat diet (55% carb, 15% protein, and 30% fat) and two different very low carb diets (both had 5% carb, 30% protein, and 65% fat). The low fat (LF) diet and one of the very low carb (LC1) diets provided a total of 1500 calories a day for women and 1800 calories a day for men. The second very low carb diet group was allowed 300 additional calories a day (1800 calories for women and 2100 calories for men). Meals were provided during the study.


After 12 weeks, all participants lost weight. Both the very low carb groups lost more weight than the low fat group (LC1: -23 lbs, LC2: -20 lbs, and LF: -17 lbs). The difference between the diets was not statistically significant. More body fat was lost than lean body mass (such as muscle) or water on all the diets. All participants lost inches from their waist and hips.


All three diets were effective in reducing weight in adults and the weight lost was primarily body fat. Even participants consuming higher calories on the very low carb diet were able to lose more weight compared to the lower calorie, low fat diet. Several risk factors for heart disease improved on all diets. The authors concluded that very low carb diets do not reduce weight only by restricting calories.


The following information was written by Atkins professionals.

Individuals followed one of three diets: a low fat, calorie controlled diet (1500 calories women/1800 men), a low carb, calorie controlled diet (1500 calories women/1800 men), or a low carb diet containing 300 additional calories a day (1800 women/2100 men). Individuals following a low carb diet (5% carbohydrate, 30% protein, 65% fat) lost weight regardless of whether calories were restricted. Weight loss in both low carb groups was greater than for those following a low fat diet (55% carbohydrate, 15% protein, 30% fat). These results suggest that a low carb diet, with or without caloric restriction, produces greater weight loss than a low fat diet.

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