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20.08.2010


Young kidneys function fine on a protein diet, old kidneys don’t

A diet containing twice as much protein as normal is not dangerous for the kidneys of young people, if you believe a study done at the Mayo Clinic School of Medicine. The same is not true for the elderly – their kidney function deteriorates measurably on a protein-rich diet.

We are living to an older age and therefore succumbing more and more to problems of old age. Researchers are looking for ways to keep the muscles of old people strong, and a potentially interesting way would be to use a diet containing more than the normal 15 percent energy derived from protein.

In their experiment, the researchers at the Mayo Clinic wanted to learn more about the effects and potential risks of such a diet, so they got 10 healthy young men and women, with an average age of 24, to follow a 10-day diet in which 30 percent of the energy came from protein. [HP] The researchers also did the same with 9 healthy elderly people, with an average age of 70.

The subjects did no sport.

Before the subjects started on the diet [UP] the researchers measured the amount of muscle protein they were making. When they repeated the measurement after the 10-day diet, they saw that the production of muscle protein [FSR] had increased in the old people and had declined slightly in the young people. The effects were not significant.





The figure above right shows why the effect is so small. The breakdown of muscle protein – measured in terms of the oxidation of leucine – also increases as a result of the protein diet. This increase is statistically significant by the way.

So can you gain more muscle without training but just by eating more protein? In young people it probably doesn’t work, and in old people it probably does work. We can’t say any more on the basis of an experiment that only lasted 10 days.

There are more clear results from a study on the effect of a protein diet on kidney function. The researchers gave their subjects a labelled substance so they could see how quickly the kidneys filtered it out of the blood and got rid of it via the urine. This enabled the researchers to calculate the glomerular filtration rate [GFR]. Some diseases and the ageing process lower the GFR. If your GFR falls below 30, you’ve got a problem. If your GFR falls below 15, then it’s time for kidney dialysis or a transplant.

The young subjects’ GFR rose, but in the seventy-year-olds it decreased. The figure below left shows the GFR before the experiment started, and below right the effect of a 10-day protein diet.



The older subjects’ kidney function was still good enough after the protein diet. But, according to the researchers, the negative trend suggests that if older people have kidney problems for whatever reason, it is inadvisable to follow a protein-rich diet. "High dietary proteins widened the differences in GFR between young and older people, causing concern about the potential adverse effect on kidney function in older people", the researchers write.

If a protein rich diet is not good for you, but you still want to build muscle, there are three things you can do. To start with you can make sure that the protein you are eating is as high quality as possible.

A second strategy is to concentrate your protein intake before and after your strength training sessions. This works better if you use fast proteins and separate amino acids. For example, you could take 18 g whey before training and immediately afterwards another 20 g whey. During your training it might help to take a pre-digested protein such as PeptoPro or good old BCAAs.

Not so keen on taking supplements? Make sure you eat a protein-rich meal an hour before training and drink a litre of a skimmed dairy product after the session.

And finally, you can increase the anabolic effect of the proteins you consume by taking amino acid supplements. Bodybuilders report good effects from 5-7 g leucine per protein-rich meal.

Particularly interesting amino acids are arginine, ornithine and citrulline. These improve the effects of strength workouts, stimulate anabolic mechanisms, and help the kidneys to remove more ammonia and broken down protein out of the blood.

Source:
Am J Physiol Endocrinol Metab. 2008 Oct; 295(4): E921-8.

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