Let’s examine the likely protein needs of each life stage – based on research findings over the past few decades. And while we’re doing that, let’s also take a critical look at current Dietary Reference Intakes (DRI) used in the US and many other countries, and how well these reflect or do not reflect such findings.
Children are programmed to grow and their bodies are expert at maximizing protein synthesis for whatever food forms they consume. With all that growth, however, they need a very high amount of protein per kilogram of body weight. As the fastest-growing individuals in terms of percentage increase in body mass, infants have the greatest need (the DRI for protein intake states 1.52g per kilogram of body weight per day for infants), while toddlers are considered to need somewhat less, at 1.05g/kg/d.
Where children are concerned, these values are probably quite accurate, in part supported by evidence from regions of the world where it has been possible to measure the effect of adding different protein levels to the diets of children recovering from malnutrition.
If the extent to which they are able to keep their bedrooms tidy were a measure of dietary requirements, most teenagers would appear to be in constant energy deficit. From a protein requirements point of view, however, they are still growing, albeit at a slowing rate, so it’s estimated that around 0.95g/kg/d is adequate for a typical activity profile.
Research tells us that healthy humans who lead ‘normal’ lifestyles, need the least protein of any age group, just 0.8g/kg/d. For the critically ill who need extra support either to recover or whose diets need constant supplementation, the DRI lists higher levels of protein from 1.2g/kg/d to 2.2g/kg/d.
Perhaps the most studied group, however, is those who participate in intense resistance exercise. Anything from martial arts, weight-lifting to heavy manual labor. Study results are varied, to say the least, ranging from no measured effect from increased protein levels to significant support for increased skeletal muscle protein synthesis and improved body composition.
Overall, however, there’s a general consensus that high-quality protein supplements and carefully planned ingestion schedules are key to building and re-building muscle mass at the limits of the body’s capability. Mixed Martial Artists, for example, are likely to benefit from intakes of around 1.6-1.8 g/kg/d, broken into around four daily meals. And if such athletes are in energy deficit, they might find further benefit from protein supplementation up to 2.2g/kg/d. Beyond this point, however, supplementation is far less likely to provide positive gains in muscle mass.
An age-old problem
What about older people? The median age in many countries, led by Japan, Germany and Italy, is increasing. Along with an aging population, a new mentality has emerged, one focused on ensuring good quality of life, characterized by a healthy mind, a healthy body and a good level of mobility.
Working against this ideal, however, are age-related declines physical activity, muscle mass and strength, the sum of which is known as sarcopenia. And studies suggest that decreased strength/muscle mass means increased risk of early death, all-cause or cancer-related, especially for those over 60 years of age. Maintaining muscle mass and strength, therefore, is key to the quality of life in its latter stages.
A combination of physical activity and protein consumption will likely slow down sarcopenia in aging populations. But a large body of data also indicates that older persons could benefit from consuming significantly more protein than the 0.8 g/kg/d the DRI suggests for the over-65s. And that’s a disturbing finding, when you consider that older people are likely to ingest less protein than younger ones, due, for example, to reduced appetite with age.
Whether you’re a professional athlete or just someone who’d like to continue playing casual golf into your twilight years, the type of protein you use to improve your life is of vital importance. Here, milk proteins – and whey protein, in particular – may be a smarter choice than soy or other plant-based proteins, for example. Milk’s effectiveness as a protein source is partly due to its combination of whey and casein proteins and consuming whey causes amino acid blood levels to rise more quickly than is the case for soy or casein. Whey also provides increased synthesis of muscle proteins when at rest compared with soy or casein, probably triggered by its high levels of the amino acid leucine.
Good to know
The “How much protein?” question is certainly a fascinating one. And the answers are still difficult to rely upon as guidance for the general population. For example, the vast majority of studies in this field include only male subjects – although there is some evidence that women can moderately improve their body composition through whey protein supplementation, too. And the effect of dietary choices is known to be highly individual, with study results usually reported as averages that may not be occur in any one person.
For now, it may be best to err on the side of caution, encouraging both older persons, sedentary lifestylers and fitness fanatics to consume a little more protein, whatever the source may be. After all, we (probably) only get one life – so let’s live it as long and as strong as we can!
This blog contains clips from the Whey & Protein Blog powered by Arla Foods Ingredients. Read more about the author here:
Professor, Director, Physical Activity Centre of Excellence (PACE), McMaster University Department of Kinesiology
About the author
Dr. Stuart Phillips, in addition to being a full Professor in Kinesiology, is also an Adjunct Professor in the School of Medicine at McMaster University. He is a fellow of the Canadian Academy of Health Sciences, the American College of Sports Medicine (ACSM) and the American College of Nutrition (ACN). His research is focused on the impact of nutrition and exercise on human skeletal muscle protein turnover. He is also keenly interested in diet and exercise-induced changes in body composition.
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