Most foods contain at least two, if not all three, of the macronutrients -- protein, carbohydrate and fat. National dietary guidelines recommend getting a certain percentage of your daily calories from each of the three macronutrients and limiting your intake of unhealthy types of fat. Figure out what percentage of total calories fat makes up in the food you are eating, and you can track your intake.
Fat provides 9 calories per gram. That's more than protein or carbohydrates, which each offer 4 calories per gram. By looking at the total number of calories in a food, as well as its fat content, you can figure out the calories from fat.
For example, a large egg contains 72 calories and 5 grams of fat. Because each gram of fat contributes 9 calories to the total, you know that 45 calories in the egg come from fat.
To determine the percentage of calories from fat, divide 45 by 72, then multiply by 100 to get the percentage. In this case, fat accounts for 63 percent of the calories in a large egg.
Breaking it Down Further
There are good fats and bad fats, and it's important to be able to determine how much of the fat in a food is an unhealthy type. Nutrition labels break this down -- in grams -- for you, so you can easily spot a food that's high in saturated fat, which you need to limit in your diet, and trans fats, which you should avoid eating.
For example, two commercially prepared chocolate chip cookies have 528 calories and almost 6 grams of total fat. Of that, about 3 grams come from saturated fats and less than 0.1 gram comes from trans fats.
Saturated fats provide 5 percent of the calories and 50 percent of the total fat; trans fats provide not even 0.1 percent of the calories and under 0.3 percent of the total fat.
Meeting National Nutrition Guidelines
Dietary Guidelines for Americans, 2010 recommends adults get 20 percent to 35 percent of their calories from fat. Most of that should come from healthy mono- and polyunsaturated fats found in fish, nuts, olive and canola oils and avocados.
The American Heart Association recommends that adults who have no risk factors for heart disease limit their saturated fat intake to less than 7 percent of their calories. For a typical 2,000-calorie diet, that's less than 16 grams of saturated fat.
For those who do have risk factors for heart disease, such as high cholesterol, the association recommends limiting saturated fat intake to below 6 percent of calories, which is about 13 grams of saturated fat. Trans fat intake should be as low as possible.
Figuring out Fresh Foods
Some foods -- such as fresh fruits and vegetables, meats and seafood -- don't come with labels. To find the fat percentages of these foods, you'll need to look them up online in a nutrient database. The U.S. Department of Agriculture's National Nutrient Database provides nutrition information for thousands of foods, including all the different types of fats they include. Locate your food in the database, then identify calories, total fat and any other type of fat you're interested in, and perform the calculation in the same way.