Q. Can too much time sitting at my desk undo the health benefits of my 45-minute gym workout?

A. Exercise is extremely important for our health. Unfortunately, if the majority of our day is spent sitting at our desk, computer, or on the couch watching television, it might undo some of the benefits of structured exercise. When we sit for many hours, the enzymes responsible for burning fat actually shut down.

Physiologists analyzing obesity, heart disease and diabetes discovered that prolonged sitting shuts down circulation of a fat-absorbing enzyme called lipase. On the other hand, standing up engages muscles and promotes the distribution of lipase. Lipase prompts the body to burn fat and cholesterol, independent of the amount of time spent exercising.

The researchers found that exercising is not as beneficial if you are going to spend the rest of the day sitting. We have to pay more attention to what we are doing when we are not at the gym.

According to the lead researcher on the study, Marc Hamilton, a professor of biomedical sciences at the University of Missouri, "The existing data, by numerous studies, are starting to show the rates of heart disease, diabetes and obesity are doubled or even tripled in people who sit a lot." One reason is because when we stand or move, the enzyme lipase helps fat move into the muscles where it can be burned. When we sit, lipase virtually shuts off. This causes our body to store more fat and can also clog arteries and cause diseases.

Standing and moving lightly will re-engage the enzymes. Since people are awake 16 hours a day, if we spend most of our day sitting, we are losing an opportunity for optimal metabolism throughout the day.

Ideally a person should engage in moderate to vigorous physical activity for 30 to 60 minutes most days. However, in addition to your regular exercise routine, get up and move around while talking on the phone. Tidy up the house while watching TV. Take frequent breaks from that computer screen to stand and walk around. Any behavior you can perform while standing rather than sitting will provide a benefit.

For those who don't engage in regular exercise, movement throughout the day still offers benefits in terms of improved metabolism, disease prevention, and fat burning.

More time standing and less time sitting is good preventive medicine.

Amy Tousman is a registered dietitian and certified diabetes educator with Nutrition Unlimited in Kailua. Hawai'i experts in traditional medicine, naturopathic medicine and diet take turns writing the Prescriptions column. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.