If you want to use exercise as a way to help you lose weight, work out immediately after you eat.
Since the only way to lose body fat is to burn more calories than you take in, exercise plays a major role in increasing the number of calories you burn. Therefore, it's obvious you can burn the greatest number of calories by exercising right after a meal. (In fact, your body continues to burn extra calories for several hours after you've finished exercising.)
This news raises two concerns. First, does exercising after eating make you so tired you can't exercise as much? And second, will exercising after eating give you stomach cramps?
If you exercise at a casual pace, you should be able to exercise even longer than normal after eating. The extra calories from the food supply your muscles with energy.
The vast majority of people who are in shape can eat and then exercise at a slow pace without suffering from stomach cramps. Exercising with food in your stomach causes your stomach and skeletal muscles to work hard simultaneously, demanding large supplies of oxygen. Blood may be shunted away from your stomach muscles and to your skeletal muscles, causing stomach muscles to go into painful spasm.
If you eat only a small amount before exercising, your stomach will not be full. Then, if you exercise at a slow pace, your heart should be able to pump enough blood to satisfy both
your stomach and skeletal muscles.
Q: My health club just installed new treadmills. Do you have any tips for using this equipment?
A: First, check the power of the treadmill. It should have at least a 1-horsepower motor and be able to reach a speed of at least 7 mph. If the motor is weaker than that, the force of your foot strike can overcome the speed of the treadmill, and the apparatus will jerk as it turns.
Always wear good running shoes when you get on a treadmill. Your feet strike the belt with great force and then roll inward. Too much inward motion can injure your knees. Good running shoes prevent injuries by deadening the force of the foot strike and limiting the inward rolling of the feet.
Begin with a speed of fewer than 2 mph to allow time for your muscles to warm up. Once you start sweating, you're ready to run more quickly. To raise your level of fitness, increase the intensity of your runs, boosting your speed by 1 mph every four minutes. Slow down when you experience shortness of breath and stop if you feel pain, discomfort or dizziness. Try again two days later with the same regimen.
For the first six weeks, it's better to stop too early rather than too late. More than 65 percent of people who drop out of exercise programs do so in the first six weeks because of an injury that could have been avoided by not exercising too hard, too soon.
Q: My sunscreen lotion is made
with something called urocanic acid. What is this?
A: The Consumer Federation of America recently announced that urocanic acid, used in some sunscreens, can cause skin cancer. But representatives of the cosmetic industry disagree.
Even if urocanic acid doesn't cause cancer, it shouldn't be in your sunscreen; it does nothing to protect you from skin cancer, wrinkles, sunburn, dryness -- or anything else. It is not even a preservative to help protect other useful chemicals in the sunscreen. All it does is add to the price.
In 1989, a study in Australia showed that urocanic acid caused skin cancer in hairless mice. Some cosmetic firms still add it to their sunscreens, staunchly defending its use by claiming that humans are different from hairless mice.
So far, the evidence is far too weak to accuse urocanic acid of causing cancer in humans. It probably doesn't. The major problem is that in putting urocanic acid in sunscreen, the cosmetic industry is guilty of placing chemicals in cosmetics that are of no value to the people using them.
Sunscreen creams, lotions and ointments should contain a chemical that will block the sun's rays. They can also contain ingredients to stabilize the sunscreen chemical so it will not be rapidly broken down. Anything else doesn't need to be there.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.