The hypothesis was put forward in a new paper published in the journal Exercise and Sports Science Reviews. The work was done by a team of researchers from the UK and Lithuania.
Among their primary data points, the researchers gleaned information from six studies on high fat diets and muscle performance. All were done in mice. The review article also inlcudes as many as 50 citations.
The paper notes that increased body weight in the form of fat can actually increase muscle size and power compared to lean controls. But this is only true when the animal, whether it be a mouse or a human, is young. As people age and remain obese, muscles become fatty, too, and decline in performance. This continues to the point where the obese mice or humans have weaker muscles than their lean peers and yet still have to carry more weight.
Fat in muscles could account for decreased function
One of the theories developed in the paper as to why this is true is that when obese subjects take in too much food, they can overrun the ability of existing adipose tissue to store that excess energy fast enough. The body then starts to create fat reserves within the muscles themselves in the form of intramyocellular lipids (IMCL).
This is especially true in the case of a high fat diet (HFD). Fat is the most energy dense macronutrient and it is far easier to take in large amounts of calories as fat than in the form of carbohydrates or protein.
The researchers postulated that there may be compensatory mechanisms in younger muscle tissue that ameliorate this IMCL buildup.
“Earlier accumulation of IMCL in old than in young-adult mice on an HFD may be due to a compensatory increase in oxidative capacity in the muscle fibers of young-adult, but not old, animals that would enhance the capacity for fatty acid oxidation. . . . Such an increased capacity for fatty acid oxidation may at least transiently stave off the accumulation of IMCL and the associated muscle dysfunction,” they wrote.
How to deal with the issue is a vexing problem, as is the whole issue of obesity, the researchers noted. The paper states that caloric restriction has been shown to work short term. It can attenuate sarcopenia, or the wasting of aging muscle fibers that can be exacerbated by IMCL buildup. But severely restricting calories has been shown to be generally ineffective as a long term strategy, as few individuals can adhere to the regimen.
Cutting methionine seen as viable strategy
The authors put forward restricting the intake of the amino acid methionine as a viable alternative.
“Methionine restriction has been described as a calorie restriction mimetic and has been found to extend lifespan and reduce age-related inflammation in rats,” they noted.
Methionine is an essential amino acid found in abundant quantities in fish, meat and dairy products. Plant proteins generally contain little of the amino acid. Reducing, but not eliminating, methionine in the diet could be an effective strategy in reversing HFD-induced muscle dystrophy, the researchers argued.
Vegan diet achieves goal
“Recent research has demonstrated that restricting methionine to 0.17%–0.25% from the normal 0.86% is the ideal range to elicit metabolic benefits without stunting growth in young-adult mice (36). In practical terms, methionine restriction can be achieved by switching to a vegan diet,” they wrote.
“Although further research is required to fully elucidate the effect of methionine restriction on IMCL and skeletal muscle lipid metabolism, methionine restriction shows promise in being able to enhance lipolysis in skeletal muscle via PGC1α-controlled mitochondrial biogenesis that is prompted by up-regulation of AMPK and SIRT1,” they concluded.
Source: Exercise and Sports Science Reviews
October 2021 - Volume 49 - Issue 4 - p 253-259; doi: 10.1249/JES.0000000000000261
A High-Fat Diet Aggravates the Age-Related Decline in Skeletal Muscle Structure and Function
Authors: Degens H, Swaminathan A, Tallis J