Low-carb v low-fat diet

Does ditching the carbs lead to a healthier heart?

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A new study discusses the advantages of a low-carb v low-fat diet and its impact on heart health.

Low-carb diets of one form or another have been on our radar for quite some time as a way to quickly shed pounds, but we haven’t known much about how these types of diets affect our heart health. A study published in the Annals of Internal Medicine last week says that compared to a low-fat diet, a low-carbohydrate diet is better not only for weight loss, but may also be better for your heart. Before we jump on the low-carb bandwagon, let’s take a closer look at this low-carb v low-fat study.

The study

This study included 148 obese men and women with healthy lipids and no history of heart disease or type 2 diabetes. They were assigned randomly to either a low-fat or low-carbohydrate diet, and they followed these diets for 12 months. All participants met with registered dietitians and received nutrition education, with emphasis on the benefits of monounsaturated fats and recommendations to limit trans fats. Those assigned to the low-fat diet were instructed to have less than 30 percent of their total calories from fat (less than 7 percent from saturated fat), while those assigned to the low-carb diet were instructed to limit their carbohydrate intake to less than 40 grams per day. Neither group was given a specific calorie goal. On average across the 12 months, participants in the low-carb group consumed about 130 fewer calories per day than those in the low-fat group.

The findings

Those in the low-fat group lost an average of 4 pounds, while those in the low-carb group lost an average of 12 pounds. The low-carb group also decreased their percentage of body fat and increased their percentage of lean mass, while body composition in the low-fat group did not change. With weight loss we might expect to see a drop in LDL, but there was no significant change in LDL cholesterol (the “bad” cholesterol) in either group. There was no significant change in HDL cholesterol (the “good” cholesterol) in the low-fat group, but HDL cholesterol increased by an average of 9 mg/dL in the low-carb group. Levels of triglycerides did not decrease significantly in the low-fat group, but did drop an average of 20 mg/dL in the low-carb group. Those in the low-carb group had lower levels of CRP (a marker of inflammation) and estimated 10-year risk for heart disease (due to the increase in HDL), while those in the low-fat group did not see these cardio protective improvements.

Numbers tell the story

It can be hard to follow a diet, especially for a period as long as a year. On average, those in the low-fat group were able to keep their fat calories under 30 percent of total calories. Those in the low-carb group, on the other hand, had a harder time sticking to the prescribed 40 grams of carbohydrate per day. Three months into the study, the average daily carbohydrate intake in the low-carb group was 81 grams, and by the end of the 12 months it had crept up to 112 grams. The fact that their carbohydrate intake crept up steadily as the year went on raises the question of how sustainable this diet may be. It is important to note that although the percentage of calories from saturated fat increased in the low-carb group due to eating fewer calories, the total amount of saturated fat they ate did not increase.

What does this reveal?

A low-carbohydrate diet may be an option for weight loss in healthy individuals. Along with weight loss may come cardio protective benefits such as lower triglycerides, less inflammation and increased HDL cholesterol. This information does not show us the whole picture. As the authors state, this study doesn’t look at how many heart attacks these participants suffered down the line, only at risk markers at one year. Considering that this study was done in individuals with healthy lipids to begin with, these findings may not apply to people with high cholesterol or heart disease. It is important to recognize that we are all different — while a low-carb diet may be beneficial for some, it may increase the risk of heart disease in others.

What does it mean for you?

A diet isn’t one-size-fit-all. If you have healthy lipids like the subjects in this study and if you think a low-carb diet could be sustainable for you, it may be a weight loss option for you. But what works for one person might not work for their neighbor. If you have high cholesterol or heart disease and want to try a low-carb diet, we recommend limiting foods high in saturated fat and monitoring your lipid levels. All healthy weight loss plans — whether low-carb or low-fat — emphasize whole foods rather than processed, lots of colorful vegetables, lean proteins and healthy fats.


Vivienne Hazzard 150x150Vivienne Hazzard graduated May 2014 from the University of Michigan School of Public Health with a Master of Public Health in Human Nutrition/Dietetics. She is currently a Dietetic Intern rotating for 4 weeks at UM Cardiovascular Medicine at Domino’s Farms.



Frankel-informal-vertical-sigThe University of Michigan Samuel and Jean Frankel Cardiovascular Center is a top ranked heart and heart surgery program among Michigan hospitals. To learn more, visit our website at umcvc.org.