Muscle itself can indeed turn into fat
Ask any personal trainer or nutritionist and they will tell you that the idea that muscle can turn into fat is a fallacy.
Muscle can only be lost through inactivity, which leads to calorie imbalance which, in turn, increases fat levels in the body. But muscle itself cannot directly turn into fat. It sounds logical right? Well, kinda...
The above explanation is quite correct, but not complete. In fact, due to enormous advances in stem cell science in the last few years, we now know that muscle cells WITHIN the muscles themselves can indeed turn into fat cells - and this effect does not need to be mediated by inactivity.
This is different - and in addition to - fat cells increasing in size within fat deposits (which are of course found OUTSIDE the muscles), due to inactivity.
Fat cells can increase in muscle tissue replacing muscle cells, effectively turning muscle into fat
To clarify the two concepts let's imagine that a woman becomes inactive while she continues to eat the same amount of food as before (or more). Due to calorie imbalance, fat cells around the thigh, butt and other areas will increase in size to accommodate the extra calories in the body. This is what we always used to know. At the same time, due to inactivity, muscle tissue will be lost ("if you don't use it you lose it").
However, what we have now found (please see research paper notes below) is that if someone is inactive OR eats an excess of fattening food, will lose muscle cells INSIDE muscle tissue and some of those cells will be replaced by fat cells INSIDE the muscle tissue - in addition to fat cells increasing in size and number inside fat deposits around the thighs, butt etc.
This means that muscle itself can indeed become fat!
In simple terms, by eating too much and not exercising, an ever larger proportion of our muscles can develop "marbling". Yes, the same stuff you see on juicy ribeye (i.e. fatty) beaf steaks.
Vitamin D (and regular exercise and protein intake) to the rescue
The major implication of "muscle turning into fat" is on people who, due to inactivity or imbalance diet, lose muscle tissue - and therefore strength - and become susceptible to falls.
Fortunately, this effect can be reduced, to some degree at least, by vitamin D supplementation, which stops muscle degradation into fat and helps maintain muscle strength.
Of course, regular exercise and avoidance of fatty, sugary or carbohydrate-rich food and replacement with protein-rich food and vegetables are the first line of defence against losing muscle tissue.
Fat means "flab" - regardless if it's found inside or outside muscles
On the other hand, the aesthetic implication of muscle turning into fat, due to eating fatty/sugary foods and/or being inactive, is that muscles themselves become "flabby", i.e. lax and soft. This is in addition, to fat increasing in size just below the skin and above the muscles, which further add to the "flabby look" (fat tissue is by definition flabby).
The solution to muscle looseness, as mentioned above, is regular exercise (especially on the vibration platform), combined with adequate protein-rich food and vegetable intake and avoidance of fat, sugar and excess carbs. This will also help with superficial/fatty tissue looseness, in combination with a good cellulite reducing treatment and/or cellulite cream.
- Paper: Nutritional factors in transdifferentiation of scheletal muscles to adipocytes
- Excerpt: "A current area of interest is the determination of factors able to promote the transition from muscle to adipose tissue. The current review has highlighted that treatment of myoblasts with fatty acids (especially oleic acid) and thiazolidindiones causes conversion to adipocytes. The molecular mechanisms mediating the adipogenic action of thiazolidinediones and fatty acids in myoblasts could involve peroxisome proliferators-activated receptor-gamma (PPARgamma and CCAAT-enhancer-binding protein C/EBP. The role of 1,25-D3 in adipogenesis is mediated at the molecular level through VDR-dependent inhibition of C/EBP and PPARgamma expression and a decrease in PPARgamma transactivation activity. Vitamin D supplementation increases muscle strength and ultimately reduces the incidence of falls. Additional research is needed to fully clarify the role of nutritional factors in adipogenesis."