Nutritional Pearls: Low Fat Diets May Actually Be Bad for You

Susan is a 55-year-old woman who recently began following a low-fat diet in order to lower her risk of heart disease. At her most recent checkup, she asks if this is the best lifestyle change she could make, or if there are any other options.

How do you advise your patient?
(Answer and discussion on next page)

Dr. Gourmet is the definitive health and nutrition web resource for both physicians and patients with evidence-based resources including special diets for coumadin users, patients with GERD/acid reflux, celiac disease, type 2 diabetes, low sodium diets (1500 mg/d), and lactose intolerance. 

Timothy S. Harlan, MD, is a board-certified internist and professional chef who translates the Mediterranean diet for the American kitchen with familiar, healthy recipes. He is an assistant dean for clinical services, executive director of The Goldring Center for Culinary Medicine, associate professor of medicine at Tulane University in New Orleans, faculty chair of the all-new Certified Culinary Medicine Specialist program, and co-chair of Cardiometabolic Risk Summit.

Answer: There is little data supporting the benefits of a low-fat diet on heart health.

While the supposed health benefits of a low-fat diet have largely been disproven, there are still those who maintain that a low-fat diet helps those with heart disease avoid heart attack, stroke, or death.

Often, these beliefs can be based on cherry-picked studies, fundamentally flawed research, or both.

The Research

Fortunately the NIH's National Heart, Lung, and Blood Institute funded the Women's Health Initiative Dietary Modification Trial, a large-scale, long term study including over 48,000 postmenopausal women who were between the ages of 50 and 79 at the start of the study in 1997 (Am J Clin Nutr 2017;106:35-43). Forty percent of the participants were assigned to a low-fat diet with a target of 20% of total daily calories from fat, while the other 60% acted as the control, following their usual diet.
_______________________________________________________________

RELATED CONTENT
Low-Fat Dairy Intake Could Influence Mental Health
Unrestricted Calorie, High-Fat Mediterranean Diet Linked to Greater Weight Loss Than Low-Fat Diet
_______________________________________________________________

In the first year of the study, those in the low-fat diet group participated in 18 sessions of a group dietary behavioral program to help them meet the program's goals of consuming 20% of their calories from fat, increasing vegetable and fruit intake to at least 5 servings per day, and increasing grain intake to 6 servings per day. After the first year the meetings continued once every 3 months through the end of the initial portion of the study in 2005. The control group received "printed health-related materials only."

The authors monitored the participants' diets by administering regular food frequency questionnaires to a representative sample of both the low-fat dieters and the control group. All of the participants responded to medical history questionnaires twice a year, which allowed the authors to monitor not only health outcomes such as heart attack or stroke but also any medications the women might take as well as when a medication was started or stopped. When necessary, the researchers were able to access the participants' medical records for verification.

The Results

In analyzing the data, the authors found some unexpected results. Those women with normal blood pressure and no history of heart disease at the start of the study were 30% less likely to experience a heart attack or need angioplasty or bypass surgery than those women who had no history of heart disease but had high blood pressure. Which sounds like a win for the low-fat diet—except those same women with normal blood pressure and no history of heart disease saw their risk of stroke increase by 29%.

For those women who did have identified heart disease at the start of the study, the low-fat diet did not affect their risk of stroke, but their risk of heart attack or needing angioplasty or bypass surgery increased by 47%. As the authors put it, "we were not able to rule out the possibility that dietary changes in [the low-fat diet group] could have contributed to their [increased risk of heart attack, angioplasty, or bypass surgery]."

Those with high blood pressure but without heart disease at the start of the study who went on the low-fat diet saw no clinically significant change in their risk of developing heart disease, having a heart attack, needing angioplasty or bypass, or indeed, death from all causes. The authors note, however, that changes in whether those participants were taking cholesterol-lowering medications or not over the course of the study could have hidden some small benefit that could be attributed to the low-fat diet.

What’s the “Take-home”?

The authors mention in their closing that they will be further analyzing the data to determine if there were certain dietary patterns that contributed to the results, and I look forward to seeing those data published. In the meantime, view with great caution the claims that a low-fat diet will keep your heart healthier.