5.10: Concentrated Source of Calories

Fat not only has more calories (9 cal/g) than carbohydrate or protein (4 cal/g), but it’s an even more concentrated source of calories. Unlike protein and carbohydrate, it doesn’t take on the water that would dilute its calories. We eat fat “dry,” and protein and carbohydrate “wet.”

Salad oil is 100% fat, making it 9 cal/g (120 cal/ Tablespoon). Butter, margarine, and mayonnaise are about 85% fat and have 7 cal/g (105 cal/T). The fat rises when butter is melted, leaving below the milky, watery portion. When this fat is drawn off the top, it’s called drawn butter, clarified butter, or dehydrated butter. The water is gone, so drawn butter has the same amount of fat (100%) and calories (120 cal/T) as oil. Lobster and crab are often eaten dipped in drawn butter.

In contrast, carbohydrate and protein hold a lot of water. Note how much water is taken up by dry rice, pasta, and beans during cooking (Table 5-1). Also, note that when bread, cooked rice, oil and meat are left uncovered, the bread, rice, and meat dry out, but oil and the fat around the meat don’t. Table 5-2 gives the fat, water, and calories in some foods to show how fat concentrates calories and how water dilutes them.*

Many of us think of starchy foods, like bread, rice, pasta, and potatoes, as fattening. They get their reputation by association—we usually eat them with fat (e.g., buttered bread, french fries).

In their natural state (not dried), carbohydrate and protein hold about 3 times their weight in water. Potatoes, bananas, and the fat-free parts of meat are about 75% water and 25% carbohydrate or protein. So their calories have been diluted to only 1 calorie per gram:

4 cal/(1 g carb or protein + 3 g water) = 4 cal/4 g = 1 calorie/gram

Thus, as normally found in food (and in our own tissues), carbohydrate and protein have 1 cal/g, whereas fat has almost 10 times more (9 cal/g). This striking difference has important implications:

• If you add 1 Tablespoon of butter to ½ cup cooked rice, you double the calories, because each has about 100 calories (Table 5-2).

Table 5-2: Fat, Water, and Caloric Content of Some Foods

In contrast, many people in developing countries don’t get enough calories because foods rich in fat (e.g., meat, cheese, oil, butter) are scarce. Diets of mainly plant foods can be too bulky for children to get enough calories. A 5-year-old child needs about 1800 calories per day. If there’s only low-fat plant food to eat, the child would have to eat the equivalent of about 26 cups of carrots or 17 bananas or 15 boiled potatoes or 8½ cups of rice to get those 1800 calories.

American children are stumped when asked, when is chocolate candy nutritious? They don’t think of candy this way. A chocolate bar has about 150 calories/oz (600 calories per ¼ lb). Rich in fat (Table 5-2), it’s a concentrated source of calories—very nutritious for a child suffering from a lack of calories. As our children dawdle over their vegetables, we sometimes tell them to think of starving children in other parts of the world. Our children would gladly send them the vegetables. But starving children are more in need of high-fat food—like the butter we put on our vegetables.

• Simplesse, a fat substitute made for low-calorie foods, is made of whey protein (from milk) shaped into tiny spheres. Protein is lower in calories and holds water, so it’s a low-calorie (1 cal/g) substitute for fat (9 cal/g). The protein is shaped to give the slippery “mouth-feel” of fat. It isn’t used in products that must be heated (e.g., cookies and crackers) because heat alters its shape and thus its feel. (As will be discussed later in this chapter, heat alters protein’s shape.)
• Fat makes hamburger juicy. How do you make a lean burger juicy? McDonalds’ McLean Deluxe burger mixed lean beef with carrageenan, a soluble fiber from seaweed. The fiber holds water, making the hamburger “juicy.” It also left out the cheese and mayonnaise-type dressing. A McLean weighed about the same as a Big Mac and but had fewer calories (320 vs. 540) and less fat (10 vs. 28 grams). Due to poor sales, the McLean was phased out in 1996.
• Fat is a concentrated source of energy, storing a lot of calories with minimal weight.† A normal-size 150-pound man has about 15 pounds of stored fat that provides more than 60,000 calories.* This many calories worth of carbohydrate weighs about 120 pounds* and would certainly affect his mobility!

^{*Adding more water to “solid” food helps in weight-loss diets. We eat less when the same ingredients are made into a soup instead of a casserole—volume is a factor in how much we eat. It’s been proposed that labels give caloric density of a food (e.g., how many calories per oz) so we aren’t confused into thinking that low-fat cookies are low-calorie; they’re high-calorie when dry and chock full of sugar.
†Migrating birds accumulate fat for flight. If they stored energy as glycogen instead, they’d have trouble getting off the ground. They store fat in their liver (“fatty liver”), a capacity used to produce the French delicacy foie gras by force-feeding duck or geese. Plants store energy mostly as carbohydrate (starch) because they’re “grounded.” Note that the plants’ seeds are often rich in fat (e.g., sesame seeds). This makes seeds light (more mobile) and easier to disperse, and provides a compact source of the initial energy the seed needs to sprout.
*15 lb fat = 6,810 grams; 6,810 g x 9 cal/g = 61,290 calories. 1 g glycogen holds about 2.7 g water; 4 cal/g glycogen + 2.7g water = 4 cal/3.7g = 1.1 cal/g; 60,000 cal/1.1 cal/g = 54,545g = 120 lb}