The average person loses 5% of their total muscle mass every decade after the age of 30. To make matters worse, loss of lean muscle mass speeds up after the age of 50. Of course, this grim scenario takes place in sedentary people who do no resistance training. Resistance training reduces the loss of lean body tissue and helps preserve bone density too. There’s an interesting phenomenon described in older people that at least partially explains why it’s more difficult to retain muscle during the later years of life. It’s called anabolic resistance. Anabolic resistance, while more common in the elderly, can also affect younger people as well.
What is Anabolic Resistance?
Anabolic resistance is the reduced ability to synthesize muscle proteins in response to a protein meal. To avoid loss of muscle tissue, the breakdown of muscle protein needs to be balanced by the synthesis or making of new muscle protein. Since people lose muscle with age, this loss must be due to either increased protein breakdown or reduced muscle protein synthesis. Research shows the most important of these two factors is the reduced ability to make new muscle proteins due to anabolic resistance.
Studies show when a young person consumes protein, as little as 10 grams is enough to stimulate muscle protein synthesis. Not so in the elderly. More than double this amount isn’t necessarily enough to boost muscle protein synthesis in older people. So why are the elderly less able to use the amino acids from dietary protein to build new muscle tissue?
There are a variety of possible reasons why anabolic resistance becomes a problem with age. For one, elderly people may not be able to digest and break down protein to amino acids as easily. This means fewer amino acids are absorbed and reach muscle tissue where they can be used. Some research suggests the delivery of amino acids to muscle tissue is reduced due to changes in small blood vessels that feed into the muscle.
Some research also suggests chronic inflammation is a factor in anabolic resistance. Some studies show that omega-3 fatty acids, being anti-inflammatory in nature, boost muscle protein synthesis in animals, and, possibly, humans too. Regardless of the cause, anabolic resistance is a serious problem because it leads to loss of muscle mass and functional strength in older people. Loss of strength and muscle tissue inevitably progresses to frailty and reduced functional capacity.
Overcoming Anabolic Resistance
If muscle loss with aging is mostly due to reduced muscle protein synthesis, is there anything you can do about it? Based on research, exercise decreases anabolic resistance and improves muscle protein synthesis. One study showed exercise, even a low-intensity aerobic workout, prior to eating a protein meal reduced anabolic resistance and boosted muscle protein synthesis. Muscle contractions, even at a relatively low intensity, before a meal seems to be effective. At the other extreme, when anyone, regardless of age, is confined to bed rest for a sustained period of time, they experience loss of muscle tissue. The lack of muscle movement and contraction greatly reduces muscle protein synthesis.
So how can older people, or anyone for that matter, deal with anabolic resistance? Do some form of exercise prior to every meal to up-regulate protein synthesis. Resistance exercise is best because it has more sustained effects on protein synthesis. In one study, resistance training increased the sensitivity of muscle cells to amino acids from protein for several days afterward. Resistance training makes it easier for muscle cells to use the amino acids you feed it to make muscle protein. Another reason to grab a pair of weights and start training no matter how old you are!
Anabolic Resistance and Dietary Factors
If anabolic resistance in older people is due to reduced ability to digest and absorb amino acids, what effect does consuming extra protein have? Research suggests consuming more protein and spreading protein intake out over the day instead of concentrating it at one or two meals is helpful. The recommended daily intake of protein for sedentary adults is 0.8 grams of protein per kilogram of body weight – but is that enough?
Recent research suggests elderly people need more than the currently recommended amount of dietary protein to reduce muscle loss. Although the optimal amount still hasn’t been established, research carried out at Purdue University suggests elderly women need 29% more protein than the daily recommendation to help reduce muscle loss. Unfortunately, older people often don’t eat enough total calories, much less protein – and how few do resistance training? No wonder sarcopenia is such a problem.
The Bottom Line?
Anabolic resistance at least partially explains why older people lose muscle mass at such a high rate. Fortunately, any type of exercise prior to a protein meal makes it easier for muscle cells to use that protein. Resistance training has a long term positive effect on muscle protein synthesis in older people. So, the key to reducing muscle loss with age is to increase the amount of protein you take in once you reach later middle-age. Also, space your protein intake evenly across the day so you’re getting an adequate amount at each meal, consume protein before your workout and again afterward to reduce anabolic resistance and maximize protein synthesis. Most importantly, do some form of resistance training regularly.
References:
Exerc Sport Sci Rev. 2013;41(3):169-173.
Medscape Family Medicine. “Anabolic Resistance of Muscle Protein Synthesis with Aging”
Exerc Sport Sci Rev. 2013 Jul;41(3):169-73. doi: 10.1097/JES.0b013e318292f3d5.
Journal of Applied PhysiologyPublished 1 May 2008Vol. 104no. 1452-1461DOI: 10.1152/japplphysiol.00021.2008.
J Cachexia Sarcopenia Muscle. Sep 2012; 3(3): 157-162.
Medscape Family Medicine. “Skeletal Muscle Protein Metabolism in the Elderly”
Int J Vitam Nutr Res. 2011 Mar;81(2-3):109-19. doi: 10.1024/0300-9831/a000061.
Purdue University. “Elderly women may benefit from higher amounts of protein”
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