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More fruit and vegetables, more muscle mass

The more potassium elderly people get from eating fruit and vegetables, the greater the percentage of their body that does not consist of fat – in other words, lean body mass. Researchers at Tufts University announced this in the American Journal of Clinical Nutrition.

Fruit and vegetables contain potassium bicarbonate, a substance that makes the body alkaline. Meat and grains by contrast contain sulphur-containing amino acids which create an acid environment in the body.

Doctors call the condition whereby there is too much acid in the body 'metabolic acidosis'. When this happens the body starts breaking down muscle fibre, in an attempt to reverse the process of acidification. The proteins and amino acids that are released end up in the liver, which converts them into glutamine. The kidneys then convert glutamine into ammonia, and ammonia neutralizes acids by taking away their hydrogen atoms.

Is it possible that this mechanism reduces muscle mass in the elderly, the researchers asked themselves. If this is the case, then a diet containing lots of potassium carbonate in the form of fruit and vegetables should protect muscle mass. To check whether this really is the case, the researchers examined four hundred elderly people with an average age of 71. They measured the concentration of potassium in their urine – a marker for the potassium carbonate intake – and determined their lean body mass (LBM).

The results are shown below. The upper line represents the men in the group, the lower line represents the women.

More fruit and vegetables, more muscle mass

The researchers divided the old people into four equal-sized groups according to the concentration of potassium in their urine. Quartile is the name given to the groups. Quartile 4 is the group with the highest concentration of potassium. And, as you can see, this group has the highest percentage of LBM.

On average the old people's intake of potassium was 3.5 g per day, which is about the same as the average western person gets, but it is only half of what we should consume, according to the Institute of Medicine. Half of the old people’s potassium came from vegetables and fruit. The highest amount of potassium consumed by the elderly was 10 g per day.

All in all, optimizing potassium intake can help elderly people to retain muscle mass, the researchers think. In theory, doubling the intake would lead to 1.6 kg more fat free mass. The average seventy-year-old loses about two kilograms of fat free mass in ten years.

Am J Clin Nutr. 2008 Feb;87(2):379-84.