If you survived through the many hazards of life up through those middle-age years, congratulations!

Many (perhaps most) of us "post-midlifers" took health and safety for granted during the first half of life. However, the second half brings some of life’s greatest challenges, such as maintaining health, physical fitness and mental sharpness.

The process of aging can uncover our genetic weak links as metabolic wear and tear creates chronic health conditions. Common conditions include heart disease, diabetes, osteoporosis, cancer, arthritis, poor dental health, etc. The good news about this natural aging process is that many of our weak links can be minimized, or at least managed, by some proactive changes in lifestyle — especially regarding nutrition and exercise.

Question: What are the key challenges of the natural aging process?

Answer: Generally there is a gradual decrease in muscle mass with aging past middle age. When it goes too far, it decreases strength, mobility and flexibility. This lean tissue loss can even compromise the immune system. Since this loss also reduces calorie needs, an increase in body fat is common.

Another very basic change for many people is a decline or loss of their normal sense of thirst. Maintaining adequate body water (from both fluids and food) is challenging when the sense of thirst changes. A chronically dehydrated state can aggravate many health problems by stressing cardiovascular and kidney functions, and can even promote muscle loss.

Another challenge is knowing how the diet may need to change. Since calorie needs decrease, a person must meet his or her nutrient requirements with fewer calories. This requires selecting lower-calorie foods that are rich in key nutrients — often called nutrient-dense foods.

Some people experience a decreased appetite. This sometimes is related to poor hydration, medications or changes in a person’s taste perception.

Q: How can a person prevent or at least slow these negative physiological effects of growing older?

A: The good news is that many of these changes can be prevented, reversed to some extent, or at least slowed by regular, daily exercise. Strength-training resistance exercises like weight lifting are not just for the younger generation. Of course, the benefits of exercise also are dependent on adequate nutrition.

Add some aerobic exercises like walking, biking, etc., and reap cardiovascular benefits along with increased calorie needs. This makes it easier to meet essential nutrient needs and maintain or achieve a healthy weight.

Research also supports what most of us know — that we feel and think better when we have daily physical activity. Mental function can improve along with physical fitness.

Q: What are the best foods to consume?

A: It really comes back to the basics of meeting nutrient needs, which requires selecting a variety of foods in reasonable proportions. An often overlooked nutrient need is for protein, which helps maintain muscle. Added protein can benefit muscle gain and fat loss.

The protein food sources with the least calories are lean meats and cottage cheese, followed by most dairy foods, beans, grains and nuts. Compared to lean meats, nuts contain about four times the calories per gram of protein.

Eat well and "use it or lose it!"

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Dobbs also works with University Health Services.