Here’s What Low-Carb Diets Do to Your Heart

4 minute read

We’re accustomed to thinking about the yin and yang of a lot of foods, from fats to carbs. But in the latest report in JAMA on carbohydrate-focused diets, researchers found that the type of carbs may not matter in lowering risk of heart disease.

Dr. Frank Sacks and his colleagues conducted a study involving 163 overweight or obese participants who followed four different diets, for five weeks each, for a total of 20 weeks. Previous studies have linked low-carbohydrate diets to a lower risk of overweight and obesity and lower risk of heart disease, but Sacks wanted to test whether it was simply reducing carbohydrates that helped the heart, or whether being vigilant about what types of carbohydrates dieters ate would make a difference.

Some studies have suggested that carbs with a low glycemic index—such as whole grains—led to fewer spikes in blood sugar, and therefore more efficient breakdown into energy, while higher glycemic index foods—including refined flours—led to larger peaks in glucose that the body couldn’t process and therefore stored as fat.

So two of the diets in the study were high in carbs overall, but one was made up of low-glycemic-index foods while the other was composed of high-glycemic-index foods. The other two diets were low in carbs overall, with the same breakdown or low- and high-glycemic items.

QUIZ: Should You Eat This or That?

Which is better for you: A 1/2 cup of ice cream or 3 scoops of sorbet?
Which is better for you: Half cup of ice cream or 3 scoops of sorbet?Getty Images (4)
Answer: A 1/2 cup of ice cream
Answer: A half cup of ice cream If you eat what you’re craving, you’re more likely to feel satisfied and eat less. And scoop for scoop sorbet contains twice the sugar with none of the filling dairy protein and fat.Getty Images (5); Gif by Mia Tramz for TIME
Which is better for you: Real butter or spray on fake butter?
Which is better for you: Real butter or spray on fake butter?Getty Images; Tara Johnson for TIME
Answer: Butter
Answer: Butter Serving size for spray butters (even low-calorie ones) are around a 1/3 second spray. What on earth does that mean? You're better off using a small amount of real butter as opposed to guessing how much you're using of the mystery melange of up to 20 ingredients.Getty Images (1); Gif by Mia Tramz for TIME
Which is better for you: A sirloin burger or a turkey burger?
Which is better for you: A turkey burger or a sirloin burger?Getty Images (2)
Answer: Sirloin burger Restaurant turkey burgers are often made with dark meat and the skin, so they’re not necessarily better for you (and for the record, they aren't low-fat). You can get a sirloin burger that’s 95% lean meat and gives you 20 g of protein. Just be careful with the toppings.Getty Images (1); Gif by Mia Tramz for TIME
Which is better for you: Almonds or pretzels?
Which is better for you: Almonds or pretzels?Getty Images (2)
Answer: Almonds
Answer: Almonds Almonds are high in protein, fiber and fat and will keep you feeling fuller longer. Give high-sodium pretzels about an hour and you'll feel hungry again thanks to the high-carb no-fat or protein content.Getty Images (1); Gif by Mia Tramz for TIME
Which is better for you: Eggs or Special K?
Which is better for you: Special K or eggs?AP; Getty Images
Answer: Eggs
Answer: Eggs In the morning, you want a meal that will fill you up. Eggs offer protein and fat for satiety, but Special K cereal really only offers carbs and, well, air. If you want carbs to kick off the day, you're better off pairing eggs with a slice of 100% whole grain toast. Getty Images (1); Gif by Mia Tramz for TIME
84505234
Which is better for you: Fat free salad dressing or regular salad dressing?Tara Johnson for TIME
Answer: Regular salad dressing
Answer: Regular salad dressingTo absorb fat soluble vitamins like Vitamins E and K in vegetables you need to consume them with a fat to aid nutrient absorption. Fat-free dressing, meanwhile, is low-calorie but gets its flavor from added sugar and salt.Tara Johnson for TIME (5); Gif by Mia Tramz for TIME
Which is better for you: A low fat cookie or dark chocolate?
Which is better for you: A low fat cookie or dark chocolate?Getty Images (2)
Answer: Dark chocolate “People tend to believe fat free is calorie free,” says Keri Gans, a registered dietitian in New York City. “Go for the real thing.” Fat free cookies may be lower in fat, but higher in other ingredients like sugar. Try a nice piece of dark chocolate for those antioxidants.
Answer: Dark chocolate “People believe fat free is calorie free,” says Keri Gans, a registered dietitian in New York City. “Go for the real thing.” Fat free cookies tend to be high in carbs, sugar and fake sugar. Try a nice piece of antioxidant-rich dark chocolate instead.Getty Images (2); Gif by Mia Tramz for TIME
Which is better for you: Low fat Greek yogurt or 100 calorie Yoplait yogurt?
Which is better for you: Low fat Greek yogurt or 100 calorie Yoplait yogurt?Tara Johnson for TIME
Answer: Low fat Greek Yogurt
Answer: 2% Greek YogurtA little fat is good in the morning to keep you full—plus it has upwards of 17g of protein per container. Fat-free "fruit" yogurt is high in sugar—7 to 10 g per serving—and lower in protein.Tara Johnson for TIME (2); Gif by Mia Tramz for TIME

“What we were thinking was that the glycemic index of the carbs would be more impactful if the total amount of carbohydrates was higher,” says Sacks. “But what we found was against what we thought originally. The low glycemic index did not improve any of the things we measured.”

In fact, among those eating the high-carb diets, those consuming low-glycemic-index foods had worse insulin response and higher LDL cholesterol. Among dieters eating the low-carb diets, the high v. low glycemic index foods did not make a difference in insulin response, blood pressure, LDL or HDL cholesterol levels.

Overall, those eating the low-carb diets had lower risk factors for heart disease compared to the group eating more carbohydrates, but the type of carbs didn’t seem to make much difference. “We confirmed previous studies that showed reducing carbs is good, but we did not show that the glycemic index of the carb really had any favorable effect,” says Sacks.

That suggests that all the attention to knowing the glycemic index of various foods—and basing your eating habits on these numbers—may not be worth the effort. While bananas may have a high glycemic index compared to an apple, for example, always choosing the apple over the banana may not lead to benefits for the heart. That’s because glycemic index is only one aspect of how we break down and metabolize food; bananas are also high in potassium and fiber, which have been linked to lowering risk of heart disease.

“Consumers should just look at the food, and not worry whether it has a low glycemic index or a high glycemic index,” says Sacks. “If it’s a fruit or vegetable, or a whole grain, then it’s fine.” He also notes that glycemic index isn’t a set characteristic of a food; it’s how an individual person’s body processes the food so it may vary considerably among different people.

People with diabetes have more trouble breaking down sugar from carbs, so it may help them to avoid foods that cause peaks of blood sugar. But for the rest of us, when it comes to eating to keep your heart healthy, it’s more important to eat healthy whole foods like fruits, vegetables, fish and whole grains, rather than trying to rank individual fruits, for example, by their glycemic index.

More Must-Reads from TIME

Contact us at letters@time.com