A patient asks: Is low-carb food the best for heart health?

The doctor answers: Being trim is best for heart health, and reducing processed carbs may help.

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Carrying extra weight, especially around your middle, is a killer. All that extra visceral fat — called that because is surrounds your viscera, or organs — compresses your blood vessels, and sends your blood pressure soaring. This stiffens and ages your arteries, making them less efficient at circulating blood. That makes your heart work harder to pump. Poor heart!

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But given that we have a taste for more sugar, more fat, more salt — this “more, more, more” appetite adds up to more pounds, and less health. So what to do?

Visceral fat — so called because is surrounds your viscera, or organs — compresses your blood vessels, and sends your blood pressure soaring.

Nowhere is there more gimmicky advice and wishful thinking than with diet. But from a strict heart-health perspective, the wise approach is fairly straightforward: more varied vegetable intake, more fruit, more fish, and less starchy breads, snacks, and sweetened drinks. This is neither a very low-fat diet nor a very low-carb diet, but a moderately low-carb diet with a heavy foundation built in the produce aisle.

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Research backs this up. Colleagues at Harvard Medical School studied 21 overweight and obese young adults (average age: 30 years old) in a setting where they ate specially prepared foods with a carefully determined nutrient composition. After achieving 10-15 percent weight loss, participants were placed on one of three diets. All three diets had the same number of calories.

The diets were:

  • Low-fat diet, with 60 percent carbohydrates, 20 percent fat, 20 percent protein — a high glycemic load.
  • Low glycemic-index diet, with 40 percent carbohydrate, 40 percent fat, 20 protein — a moderate glycemic load.
  • Very low-carbohydrate diet, with 10 percent carbohydrates, 60 percent fat and 30 percent protein — a low glycemic load.

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After four weeks, the participants switched diets, and after another four weeks they switched again. Each participant spent four weeks on each of the three diets.

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The most striking finding was that resting energy expenditure (the old “basal metabolic rate”) and total energy expenditure actually fell on the low-fat diet, even though the diets were all equal in calories. Resting and total energy expenditure were intermediate with the low-glycemic index diet, and highest with the very low-carbohydrate diet.

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What does this mean? Somehow the body senses fat and carbohydrate differently, and it resets the thermostat to a lower “burn rate” when we eat a low-fat diet. The lower burn rate (lower resting and total energy expenditure) means the low-fat diet causes the body to slow down its metabolic rate, thereby resisting further weight loss.

This might make sense from an evolutionary standpoint, as a way of avoiding starvation and preserving our body fat and muscle stores. But today, when many of us want to lose weight (and are not worried about starvation), the low-fat diet may be counterproductive by slowing our metabolic rate. You can counter this slowing of the metabolic rate, of course, by increasing your exercise, but you would have to exercise for many hours each day — four to six hours — to offset the lower metabolic rate while sitting, resting and sleeping.

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While a very low-carbohydrate (10 percent) diet is often promoted as the fastest bullet train to weight loss, I do not recommend this approach. Not only is it impractical, it too often is interpreted as discouraging fruit consumption, which is not just bad for heart health but bad for sustainable weight maintenance.

Research shows that each extra (1/2 cup) serving of fruit you eat a day reduces the risk of heart disease by 7 percent. (I eat about two cups of fruit a day on my moderately low-carb diet.) French researchers analyzed nine studies involving more than 220,000 individuals and found the risk of cardiovascular problems declined as fruit intake increased. They also found an 11 percent drop in stroke risk per extra fruit serving consumed.

I eat about two cups of fruit a day on my moderately low-carb diet.

Extreme low-carb diets that scrimp on fruit also scrimp on the fiber, nutrients and antioxidants that fruit contains. By “starving” your body of such nutrients, your body will naturally crave more food, making a reduced-calorie diet nearly impossible to maintain in the long run.

So avoid the fads and the “bads” — bad carbs that concentrate calories without bringing along the nutrient payoff that Mother Nature’s bounty of fruit, vegetable, nuts and beans provide.