Could a low-carb diet help your heart?

When many people think of a low-carb diet, they picture plates piled high with red meat, bacon, and butter. Low-carb diets, so often rich in saturated fat, have long been viewed as unhealthy for your heart. But a study published online Sept. 28, 2021, by The American Journal of Clinical Nutrition found that a bit more saturated fat might be okay, if the dietary mix is otherwise healthy.

The researchers determined that a carefully constructed low-carbohydrate eating plan appeared to reduce some risk factors for cardiovascular disease. This is despite the fact that 21% of the daily calories came from saturated fat, more than double the recommended daily amount.

But that doesn't mean you should push all the bread off your plate. Teresa Fung, adjunct professor in the Nutrition Department at the Harvard T.H. Chan School of Public Health, says it's premature to conclude that a low-carb approach is truly heart-healthy. One reason for caution is that the researchers chose a low-carb eating plan that wasn't necessarily typical. "This low-carb diet was not bacon and steak. This was nuts and lentils, vegetarian sloppy joes, and salmon, along with a fair number of vegetables," she says.

The study also lasted just 20 weeks, so a low-carb diet might not produce the same benefits if studied over a longer period. In addition, the research looked only at measurements of risk factors for cardiovascular disease — not actual events, such as heart attacks or strokes.

About the study

To come to their conclusions, study authors looked at a group of 164 participants, 70% of them women, who had just lost between 10% and 14% of their body weight on a structured diet. They were assigned to one of three diet plans designed to help them maintain their new weight. Each diet had the same proportion of protein — 20% of daily calories — but different proportions of carbohydrates and saturated fat. They included

• low-carb diet, which was 20% carbo­hydrate and 21% saturated fat
• moderate-carb diet, which was 40% carbohydrate and 14% saturated fat
• high-carb diet, which was 60% carbo­hydrate and 7% saturated fat.

The researchers gave each participant prepared, customized meals to help them stick to the plan. They tracked changes in various measures that indicate cardiovascular risk before and after the study period.

The researchers computed a composite score called lipoprotein insulin resistance (LPIR) to gauge each participant's cardiovascular risk. This score takes into account a combination of factors, including the characteristics of lipids (fats) in the blood and markers of insulin resistance (how well the body uses insulin to convert food into energy). The study authors concluded that the low-carb diet did better than the moderate- and high-carb diets in improving this LPIR score.

Analyzing the diet plans

But while the low-carb diet saw the best outcomes in this trial, Fung says that this type of diet might not necessarily be the best approach for many people. While the diet included many healthy foods, it was still fairly restrictive.

"This diet may be difficult for many people to follow over a long period of time," says Fung. "Imagine life with very little bread, rice, or potatoes."

The moderate-carb approach, which allowed 40% of calories from carbohydrates, may represent a more realistic approach, she says.

"The moderate carbohydrate plan contained about the same carb amount in a typical American diet, which consists of 50% carbs on average," says Fung.

The moderate diet used by the researchers permitted more variety — an English muffin, a slice of bread, or a small amount of rice, she says. The low-carb diet ruled out dessert, but the moderate-carb diet slipped in the occasional slice of cake or pie. "That might be a more realistic level for people to strive for," says Fung. "No matter how wonderful the healthy factor is for a diet, it doesn't matter if people can't stick to it."

A Mediterranean-style diet, long promoted for its health benefits, can easily fit into this moderate daily carbohydrate range, she says. It includes lean meats, olive oil, fish, nuts, fruits and vegetables.

Applying the results

The bottom line is that while it can be beneficial to reduce the carbohydrates in your diet, particularly those that come from processed or refined foods, choosing the right diet for your lifestyle and personal preferences also matters.

There are two points to consider if choosing an eating plan, says Fung.

1. Is it healthy? Consider what you are eating, not just how many carbs the foods include. A low-carbohydrate plan that is heavy in butter and other animal products is going to be far riskier than a low-carbohydrate model that focuses on vegetables and healthy fats, such as nuts and olive oil.

2. Is it sustainable? Ask yourself whether you can stick to the diet for years on end. A healthy eating plan is a lifestyle, not a short-term fix.

"The general message is when it comes to cutting carbs, there's a healthy way to do it and an unhealthy way to do it," says Fung. "I would say that over all, there is not one single diet that is best. Find the right diet for you — one that is not only healthy, but sustainable."

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