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Comparison of High-Fat and High-Protein Diets with a High-Carbohydrate diet in Insulin-Resistant Obese Women

McAuley, K.A., Hopkins, C.M., Smith, K.J., et. al., “Comparison of High-Fat and High-Protein Diets with a High-Carbohydrate diet in Insulin-Resistant Obese Women,” Diabetologia, 48(1), 2005, pages 8-16.

The following information is available at Pub Med and was not written by Atkins professionals.

AIMS/HYPOTHESIS: A diet low in saturated fatty acids and rich in wholegrains, vegetables and fruit is recommended in order to reduce the risk of obesity, cardiovascular disease and type 2 diabetes mellitus. However there is widespread interest in high-fat ("Atkins Diet") and high-protein ("Zone Diet") alternatives to the conventional high-carbohydrate, high-fibre approach. We report on a randomised trial that compared these two alternative approaches with a conventional diet in overweight insulin-resistant women.

METHODS: Ninety-six normoglycaemic, insulin-resistant women (BMI >27 kg/m(2)) were randomised to one of three dietary interventions: a high-carbohydrate, high-fibre (HC) diet, the high-fat (HF) Atkins Diet, or the high-protein (HP) Zone Diet. The experimental approach was designed to mimic what might be achieved in clinical practice: the recommendations involved advice concerning food choices and were not prescriptive in terms of total energy. There were supervised weight loss and weight maintenance phases (8 weeks each), but there was no contact between the research team and the participants during the final 8 weeks of the study. Outcome was assessed in terms of body composition and indicators of cardiovascular and diabetes risk.

RESULTS: Body weight, waist circumference, triglycerides and insulin levels decreased with all three diets but, apart from insulin, the reductions were significantly greater in the HF and HP groups than in the HC group. These observations suggest that the popular diets reduced insulin resistance to a greater extent than the standard dietary advice did. When compared with the HC diet, the HF and HP diets were shown to produce significantly (p<0.01) greater reductions in several parameters, including weight loss (HF -2.8 kg, HF -2.7 kg), waist circumference (HF -3.5 cm, HF -2.7 cm) and triglycerides (HF -0.30 mmol/l, HF -0.22 mmol/l). LDL cholesterol decreased in individuals on the HC and HP diets, but tended to fluctuate in those on the HF diet to the extent that overall levels were significantly lower in the HP group than in the HF group (-0.28 mmol/l, 95% CI 0.04-0.52, p=0.02). Of those on the HF diet, 25% showed a >10% increase in LDL cholesterol, whereas this occurred in only 13% of subjects on the HC diet and 3% of those on the HP diet.

CONCLUSIONS/INTERPRETATION: In routine practice a reduced-carbohydrate, higher protein diet may be the most appropriate overall approach to reducing the risk of cardiovascular disease and type 2 diabetes. To achieve similar benefits on a HC diet, it may be necessary to increase fibre-rich wholegrains, legumes, vegetables and fruits, and to reduce saturated fatty acids to a greater extent than appears to be achieved by implementing current guidelines. The HF approach appears successful for weight loss in the short term, but lipid levels should be monitored. The potential deleterious effects of the diet in the long term remain a concern.

The following information was written by Atkins professionals.

Overweight, insulin resistant women were instructed to follow either a high carb/high fiber (HC) diet, the Atkins Diet (HF), or the Zone Diet (HP). Participants were all given instruction and guidance for 16 weeks, but had no contact with the researchers for the remaining 8 weeks. Individuals in the HF group were instructed to follow Induction for the first two weeks, and then continue to Ongoing Weight Loss through week 8, with no more than 50 grams a day consumed. Carbohydrate allowance was to continue to increase in 5 gram increments through week 16, followed by consumption of an amount that would maintain weight  through week 24. Results indicated that the HF and HP groups lost significantly more weight than the HC group. Researchers noted that individuals in the HP group actually ate more fat and less protein than they were instructed, and their protein intake was similar to the HF group. These results support that controlled carbohydrate nutrition is effective in producing weight loss, and is superior to conventional weight loss recommendations.