Updated June 08, 2015.

Often when diets are compared, especially when weight loss is involved, it’s hard to tell if changes in health indicators (such as blood pressure or triglycerides) are due to the diet itself or the resulting weight loss. This study from Ronald Krauss and his colleagues attempts to address this issue.

Capsule Summary

Four groups of men eating different carbohydrate levels and different levels of saturated fat were followed for changes in blood lipids (cholesterol and triglycerides).

First, they all ate the same diet, then they were divided into the different diet groups -- first without weight loss, then with reduced calories.

Overall results:

1. The low-carb groups improved on most of the parameters of cholesterol and triglycerides, even without weight loss.
2. With weight loss, there was further (but smaller) improvement in the low-carb groups, and the high carb group partially caught up, but not all the way.
3. These trends included LDL particle size, with the low-carb groups going in the “good” direction. Additionally, the group that was higher in saturated fat had the greatest increase in particle size. More Information about Cholesterol and Low-Carb Diets, including particle size
4. Most of the changes with the “medium carb” diet were intermediate between the higher and lower carb diets.
5. On a calorie intake designed to keep weight stable, the low-carb groups still lost weight.

More Details About the Study

178 men participated in this 13-week study.

Phase 1 (Baseline): During Week 1, everyone ate the same diet.

which was 54% carbohydrate, 16% protein, and 30% fat, similar to standard recommendations such as the Food Pyramid.

Phase 2 (Diet Changed, Weight Same): During the next 3 weeks, the participants were each assigned to one of four diet groups:

1. same diet as first week
2. 39% carbohydrate with low (7% to 9%) saturated fat (essentially the Zone Diet)
3. 26% carbohydrate with low saturated fat (perhaps similar to Phase Two of the South Beach Diet, depending on the individual)
4. 26% carbohydrate with 15% saturated fat (perhaps similar to Atkins Ongoing Weight Loss Phase, again depending on the individual)

The goal in this phase was for the participants to eat the same amount of food, but change the composition of the diet, thus attempting to find the effects of diet change without weight loss.

• Phase 2 Results: Except, oops, despite the researcher’s best efforts to keep the calories up, the 26% carb groups lost weight anyway –- a little over 2 pounds for the low-saturated fat group and about a pound for the higher sat fat group (and no, it wasn’t all water weight, as the body fat percentages of the people in the low-carb groups also decreased). Even taking weight loss into account, the 26% carb groups had improvements in triglycerides, HDL, total cholesterol, apolipoprotein B, and the ratio of total:HDL cholesterol not accounted for by the weight loss. Also, increases in LDL particle size, particularly in the higher saturated fat group.

Phase 3 (Diet Same, Weight Changed): In this Phase, the idea was to induce weight loss, but keep the diet the same. So they cut 1000 calories per day out of all the diets, but kept the ratios of carbohydrate, protein, and fat the same (Note, however, that this meant a further reduction in carbs for all groups). This was sure to induce weight loss, and it did.

• Phase 3 Results: The lower-carb groups made further, but smaller, improvements. The high-carb group also improved, but not as much as the low-carb groups. The 39% carb group was intermediate on most measures.

Note: As Michael Eades points out in his analysis of this study, the report doesn’t specify the exact amount of carbohydrate, protein, and fat the participants ate. From a low-carb perspective, this is important. Dr. Eades makes an educated guess about what exactly they were eating and makes some important points about the study.

Interesting Insights From This Study

Further confirmation that low-carb diets are helpful, even without weight loss. This is important for people who aren’t overweight, but respond to low-carb diets for health problems such as high blood pressure, glucose tolerance problems such as reactive hypoglycemia, or other risk factors for heart disease or diabetes. This is also important for people who are overweight, but at their lowest sustainable weight, which is in part genetically determined.

Further confirmation that simply reducing carbohydrate tends to reduce weight, without any other intervention.

Showing that LDL particle size rises with low-carb diets alone, without increasing saturated fat, but increases even more with more saturated fat.

_{Source:
Krauss, Ronald, et al. “Carbohydrate, Weight Loss, and Atherogenic Dyslipidemia.”American Journal of Clinical Nutrition 2006 May;83(5):1025-31.}