Normally the topics of discussion in this blog center around carbohydrates. But for something completely different, this time we'll discuss another macronutrient--protein. Recently Donald Layman published an article in Nutrition & Metabolism entitled Dietary Guidelines Should Reflect New Understandings about Adult Protein Needs. His findings are so interesting that I've decided to summarize them here. Links that back up each point can be found in the list of references at the end of his article.
Layman begins by discussing the fact that protein has traditionally been thought of as an expensive nutrient. While that's true in the context of managing animals in a feedlot, it is a little less true in a human society where families are willing to pay $5.00 for a box of breakfast cereal. Nevertheless, because we have been conditioned to think in terms of eating small amounts of protein, it is important to establish how much protein is enough.
The Institute of Medicine, Food and Nutrition Board, has established a recommended daily allowance (RDA) between 0.36 grams and 1.1 grams of protein per pound of total body weight. The important aspect of the protein RDA is that it is proportional to current body weight. It is not a percentage of daily caloric intake. In other words, a man who weighs 200 pounds needs to eat a minimum of 72 grams of protein daily. It doesn't matter if his typical caloric intake is 3000 calories per day or if he is dieting and eats only 1000 calories per day. Regardless of his total caloric intake, he should be careful to consume at least 72 grams of protein every day.
Layman points out that the Nutrition Board has not identified an upper risk limit for the amount of protein a person can consume in a day. In other words, a normally healthy person should be able to eat as much protein as he or she wants to. With that in mind, let's take a look at some of Layman's observations in this article.
1. Protein provides a greater satiety value than fats or carbohydrates and reduces food intake at subsequent meals. This effect is seen when protein intake is over 30 grams at a meal, is strongest when the protein is consumed at breakfast and is weakest when it is consumed in the evening.
2. Compared with high-carbohydrate/low-fat/low-protein diets, weight loss diets with higher protein increase thermogenesis and increase the rate of fat loss. When combined with exercise, weight loss diets that are rich in protein can reduce lean tissue loss from 35% to less than 15% and protect from bone loss as well.
3. In children and young adults, skeletal muscle synthesis is regulated by insulin secretion and caloric intake. However, in older adults, this switches to a pathway regulated by the essential amino acid leucine. To protect themselves from age-related loss of lean muscle, it is important for older adults to eat more than 30 grams of protein at least two or three times a day.
4. Exercise, calcium supplements and vitamin D are important for the prevention of osteoporosis. However, in the elderly, it has been found that calcium supplements will not be effective against osteoporosis unless the daily protein intake is greater than 0.55 grams per pound of total body weight.
5. In type 2 diabetics, replacement of dietary carbohydrates with protein has been observed to decrease hyperglycemia, reduce post-prandial hyperinsulinemia, and improve HbA1c.
As the wise man said...getting old is definitely better than the alternative. But perhaps these recent studies have shown us that the symptoms of aging can be slowed down a bit in people who are willing to eat more protein.
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