If you want to make sure your muscles stay stronger longer, you don't just want to do strength-training and aerobics and eat lean and plant-based proteins (though of course, those things are beneficial).

A study published in the journal Gut says that you also want to eat plenty of prebiotic foods such as chicory root, legumes, lentils, onions, garlic, asparagus, oats, bananas, strawberries, and citrus — all of which are loaded with inulin, resistant starches, and soluble fiber.

Those nutrients support a gut bacteria called Roseburia inulinivorans. And when those microbes are happy, your muscles are happy.

Researchers looked at stool samples from 90 healthy 18- to 25-year-olds, and 33 people ages 65 and older and measured their grip strength, leg-press, and bench-press performances, as well as oxygen consumption while exercising (called VO2 max).

Roseburia were the one group of bacteria that was associated with greater strength and muscle mass.

The older subjects who had Roseburia inulinivorans in their stool samples had 29% higher grip strength and their peak oxygen intake didn't go up, indicating better fitness.

In the younger group, the presence of these bacteria increased leg-press, bench-press, and hand-grip strength.

Of course, these findings may be a "Which came first, the chicken or the egg?" situation. But I suspect the bacteria improve muscle strength, and stronger muscles help nurture the bacteria.

To take advantage of this two-step dance, aim for 300 minutes of aerobic and strength-building exercise each week, and load your diet with a good supply of those prebiotic foods.

For great recipes that include these nutrients, check out my "What to Eat When Cookbook."