The choice is clear . . . NOT
Low-fat and low-carb diets produce equal weight loss and improvements in insulin resistance but the low-carb diet may be detrimental to vascular health, according to a new study
Researchers in the the UK studied 24 obese subjects—15 female and 9 male—randomized to eat either a low-fat (20% fat, 60% carbohydrate) or low-carb (20% carb, 60% fat) diet over 8 weeks. Average age was 39; average body mass index was 33.6. Most of them had prediabetes. Food intake was calculated to result in a 500 calorie per day energy deficit (a reasonable reduced-calorie diet, in other words). Study participants visited a nutritionist every other day, and all food was provided in exact weighed portions.
Both groups lost the same amount of weight, about 7.3% of initial body weight.
Triglycerides dropped by a third in the low-carb group; unchanged in the low-fat cohort. Changes in total cholesterol, LDL cholesterol, and HDL changes were about the same for both groups.
Systolic blood pressure dropped about 10 points in both groups; diastolic fell by 5 in both.
“Aortic augmentation index” fell significantly in the low-fat group and tended to rise in the low-carb group. According to the researchers, the index is used to estimate systemic arterial stiffness. [In general, flexible arteries are better for you than stiff ones. “Hardening-of-the-arteries,” etc.] The low-fat group started with a AAI of 17, the low-carb group started at 12. They both ended up in the 13-14 range.
Peripheral insulin sensitivity improved significantly only in the low-carb group but “there was no significant difference between groups.” No difference between the groups in hepatic (liver) insulin resistance.
Fasting insulin levels fell about 20% in the low-fat group and about 40% in the low-carb group, a difference not reaching statistical significance (p=0.17).
The Authors’ Conclusions
This study demonstrates comparable effects on insulin resistance of low-fat and low-carbohydrate diets independent of macronutrient content. The difference in augmentation index may imply a negative effect of low-carbohydrate diets on vascular risk.
Yes, you can indeed lose weight over eight weeks on both low-fat and low-carb diets, if you follow them. So diets DO work. No surprise.
Loss of excess body fat by either method lowers your blood pressure. No surprise.
Once again, concerns about low-carb/high-fat diets adversely affecting common blood lipids—increasing heart disease risk—are not supported. No surprise
Hyperinsulinemia and insulin resistance are risk factors for development of diabetes and cardiovascular disease. Results here tend to favor the low-carb diet. I have to wonder if a study with just twice the number of test subjects would have shown a clear superiority for the low-carb diet.
The authors imply that aortic augmentation index is an important measure in terms of future cardiovascular health. A major conclusion of this study is that a change in this index with the low-carb diet might adveresly affect heart health. Yet they don’t bother to discuss this test much at all. I’m no genius, but neither are the typical readers of Diabetes. I doubt that they are any more familiar with that index than am I, and I’d never heard of it before.
[Feel free to educate me regarding aortic augmentation index in the comment section.]
Unfortunately, many readers of this journal article and the associated news releases will come away with the impression, once again, that low-carb diets are bad for your heart.
I’m not convinced.
Steve Parker, M.D.
Bradley, Una, et al. Low-fat versus low-carbohydrate weight reduction diets. Effects on weight loss, insulin resistance, and cardiovascular risk: A randomized control trial. Diabetes, 58 (2009): 2,741-2,748.
Nainggolan, Lisa. Low-carb diets hit the headlines again. HeartWire, December 11, 2009.