The term "calories from fat" refers to the percentage of calories in a serving of food that come from fat rather than from carbohydrates or protein. This figure is listed on nutrition labels for most foods.
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The percentage of calories a person gets from fat versus carbohydrates makes little difference in terms of weight maintenance or weight loss. However, two studies published in the journal "Obesity" in 2007 suggest that a person who consumes a lot of calories from trans fats may be more likely to gain weight compared with someone who consumes calories from other types of fats or from carbohydrates or proteins.
The U.S. Institute of Medicine recommends that Americans consume about 20 to 35 percent of their total calories from fat. Every gram of fat contains nine calories. This means a person who eats 2,000 calories a day should consume fewer than 78 g of fat per day.
Calories from Fat Versus Calories from Carbohydrates
People who are trying to maintain or lose weight should focus on the total calories and fat consumed rather than on whether the calories come from fat, carbohydrates or protein. "It's pretty clear that the source of the calories is really not important," said Walter Willett, chairman of the department of nutrition at Harvard School of Public Health, in a July 2008 "Time" magazine article.
Total Calories Versus Calories from Fat
When looking at the percentage of calories that come from fat, it is important to consider total calories per serving. A food that gets 60 percent of its calories from fat--a large amount--may not be unhealthy if the total number of calories per serving is low. For instance, a food that has 60 calories per serving but gets 60 percent of its calories from fat has only 4 g of fat per serving.
An Exception: Trans Fats
The percentage of a calories a person gets from fat may matter when it comes to trans fats. A study published in "Obesity" in 2007 by Kylie Kavanagh, of Wake Forest University School of Medicine, and others found that male monkeys fed a diet high in trans fats over the course of six years gained 7.2 percent of their body weight, compared with monkeys fed a low trans fat diet and gained about 1.8 percent of their body weight. Consumption of trans fats may, therefore, cause greater weight gain compared with consumption of other types of fats.
Some scientists argue that a diet that gets a high percentage of calories from fat and protein--in other words, a diet low in carbohydrates--actually may be a more effective weight-loss regimen and be more heart-healthy than low-carbohydrate regimens. In an article published in "The New York Times Magazine" in 2002, Eleftheria Maratos-Flier, M.D., who directs obesity research at Harvard's Joslin Diabetes Center, said, "For a large percentage of the population, perhaps 30 to 40 percent, low-fat diets are counterproductive. They have the paradoxical effect of making people gain weight."