I’m sure you’ve heard it before, animal protein is “complete” and plant protein is “incomplete.” Protein is made up of amino acids and 9 amino acids are considered “essential” because they cannot be synthesized by your body and must be derived from the food you eat. Animal protein has been referred to as “complete” because it contains all 9 essential amio acids. Because it is widely believed that plant protein is deficient in some essential amino acids, it has been referred to as “incomplete.”

This “incomplete protein” myth was popularized by Francis Lappe’s book, Diet for a Small Planet, in which she advocated the practice of “food combining” for vegetarians, such as eating rice with beans, so that the essential amino acids from different foods would combine to form a complete protein. She later retracted her belief in “food combining” stating in subsequent editions of the book,

“In 1971 I stressed protein complementarity because I assumed that the only way to get enough protein … was to create a protein as usable by the body as animal protein. In combating the myth that meat is the only way to get high-quality protein, I reinforced another myth. I gave the impression that in order to get enough protein without meat, considerable care was needed in choosing foods. Actually, it is much easier than I thought.

With three important exceptions, there is little danger of protein deficiency in a plant food diet. The exceptions are diets very heavily dependent on fruit or on some tubers, such as sweet potatoes or cassava, or on junk food (refined flours, sugars, and fat). Fortunately, relatively few people in the world try to survive on diets in which these foods are virtually the sole source of calories. In all other diets, if people are getting enough calories, they are virtually certain of getting enough protein.”

Here’s where it gets interesting. The idea that plant based foods were deficient in certain amino acids was based on studies of the growth of young rats done in the early 1900’s. A subsequent study done in 1952, looked at human requirements for essential amino acids and found them to be very different from rats. Additionally it showed that the requirements for all the essential amino acids in humans could be met by many unprocessed plant foods, without combining, in excess of the recommended levels. The bottom line is that plant protein is “complete.” Vegetables and grains contain all essential amino acids and non-essential amino acids in varying proportions, and will supply in excess of what is necessary for your daily needs.

A diet strategy used by Hollywood celebs, including Janet Jackson and Jessica Alba, is to include a serving of protein with every meal, about 30% of total calories consumed. Studies show that higher protein diets (30% protein) not only help with initial weight loss but also help keep the weight off.

Why does protein help with weight loss?

1. Preserve muscle mass as you lose weight. When you lose weight on any diet, you lose both fat and muscle. Higher protein diets (30% protein), however, do a better job at preserving muscle mass and your metabolism. Remember one pound of muscle burns approximately 30-50 calories per day so you want to keep your metabolism up by preserving as much muscle as possible.
2. Promote loss of body fat. Higher-protein lower-carb diets promote loss of body fat, due to the lower insulin response of a lower carbohydrate diet. Remember more insulin promotes packing on fat.
3. Metabolic advantage of protein. There is a caloric cost of digesting food called the thermogenic effect and the caloric cost is highest for protein. It takes about 30% of a protein’s caloric value to digest it, while it only takes about 2% of a fat’s caloric value. Our bodies are a lot less efficient at digesting protein, compared with carbs and fats, so less overall calories are available to the body.
4. Protein helps curb appetite. Protein makes you feel “full” and curbs your hunger more effectively than carbs or fat.

Remember balance is the key. Your body also needs carbs and fats for optimal health. While these stars incorporate protein with every meal, their diets are also rich in unprocessed carbs and healthy fats to keep their bodies in top form.