Yes, says a convincing treatise from Donald K. Layman of the Food Science and Human Nutrition department of the University of Illinois.
Layman presents four emerging concepts in protein nutrition that he thinks should be reflected in updated dietary guidelines:
Protein is a critical part of the adult diet
Protein needs are proportional to body weight; not energy intake
Adult protein utilization is a function of intake at individual meals
Most adults benefit from protein intakes above the minimum RDA
Let's take a look at the first two of these suggestions today.
Importance of Protein
Layman notes that the current Recommended Daily Allowance for protein (0.8 g/kg of body weight) is based, in part, on the premise that "once substrate requirements for essential amino acids are met, then the need for protein is satisfied." But Layman seems to suggest that protein requirements should consider more than protein's role as a macronutrient.
Protein Needs are Proportional to Bodyweight
The government's MyPyramid suggests macronutrient guidelines in percentages of energy intake:
Carbohydrates 55%
Fats 30%
Protein 15%
While this may satisfy the minimum RDA requirement for some people, Layman argues that when energy intake is reduced - as it is when dieting or as people age - the need for protein increases. He suggests protein need is actually inversely proportional to energy intake, driving an increase of about one percent for every 100 kcal decrease in energy intake below 2000 kcal/day.
That dieting and ageing may both increase dietary protein needs may not be surprising to you, as I have discussed this before. But Layman presents some excellent supporting evidence worth discussing further.
Dieting and Protein Intake
To quote Layman, "...long-term success with weight loss relates to maintenance of metabolically active lean tissues and research has proven that higher protein diets protect muscle and bone during weight loss." And of course, we know lean muscle is not only crucial for successful, long-term weight loss, but for everything from immune function and injury prevention to overall health and mortality rates.
Age and Protein Intake
Layman states that although the need for total protein may not increase with age (in terms of proportion of the diet), our bodies require more essential amino acids in order to promote lean muscle growth and maintanence. Our bodies may need to take in more protein because of less efficient protein absorption and an increased dependency on amino acids - as opposed anabolic hormones - to stimulate muscle.
He explains, "After approximately age 30y, the anabolic drive is lost; basal levels of hormones become largely ineffective in stimulating protein synthesis in structural tissues; and diet quality and physical activity become the limiting factors for maintaining optimal protein turnover for repair, remodeling, and recovery."
The loss of lean muscle due to ageing, also called sarcopenia, is negatively associated with our ability to fight disease, recover from injury and live independently. Researchers are now also uncovering the connection between muscle loss and bone loss, known as osteoporosis. And while it was previously feared that increasing protein intake could promote bone loss, Layman notes that protein increases intestinal calcium and supports bone matrix turnover.
In my next post we will look at the last two of Layman's recommendations for new protein guidelines. Until then, let me know your thoughts on the first two. Do you agree with Layman's assessment?
