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Restrict Protein, Not Just Calories, to Prolong Life

Recent research show that protein restriction may be far more effective than calorie restriction in prolonging the lives of humans. Many studies show that restricting calories prolongs the lives of yeast, worms, spiders, flies, insects, rats and probably monkeys. Humans who severely restrict calories have long-life characteristics, such as low cholesterol and blood pressure and hearts that are more than 15 years younger than those of other North Americans their age (Experimental Gerontology, August 2007).

However, most of the test group of humans who restrict calories do not have a drop in a hormone called Insulin-Like Growth Factor-1 (IGF-1) that appears necessary for living a long time. High blood levels of IGF-1 are associated with premature aging and diseases of aging such as diabetes and cancer. IGF-1 levels are lower than normal in worms, flies and mice on restricted-calorie diets, but not in humans. This week a report shows that IGF-1 shortens life by increasing cell DNA genetic damage, and causes cancer by blocking apoptosis that causes cancer cells to kill themselves before they destroy their host (Science Translational Medicine, February 16, 2011).

Luigi Fontana, a professor of medicine at Washington University in St Louis, noticed that most calorie-restricting humans eat high levels of protein, about 1.7 grams per kilogram of body weight/day. This is more than the US government-recommended intake of 0.8 g/kg/day, and even higher than the 1.2 g/kg/day that the average American eats. Dr. Fontana asked humans on calorie restricted diets to reduce their intake of protein to 0.95 g/kg/day. After just three weeks of reduced protein intake, their IGF-1 levels dropped markedly (Aging Cell, September, 2008).

Among the calorie-restricting humans, vegans have lower levels of IGF-1 than meat-eaters (Rejuvenation Research, February 2007). Strict vegans also have significantly lower IGF-1 levels than people who restrict just calories, even if they are heavier and have more body fat. Strict vegans take in about 10 percent of their calories from protein, whereas those on calorie restriction tended to get 24 percent of calories from protein. Other data show that diets lower in protein might protect against some cancers. So restricting protein may be more important than restricting calories.

If fruit flies and rodents are fed special diets that restrict protein, they can eat as many calories as they want and still live longer (Nature, December 2009). This suggests that as long as you are not overweight, you may not need to restrict calories. Instead, restrict only protein which is far easier to do.

Furthermore, you can probably eat all the fruits and vegetables you want and not restrict calories as long as you restrict protein. That's very good news because it is far easier to restrict protein than it is to restrict all foods. The only way that you can restrict calories and still remain healthy is to eat a diet based on vegetables. It now appears that you extend your life far more by reducing protein that you would by restricting just calories.


Dear Dr. Mirkin: Is there an advantage to taking cold drinks when racing in very hot weather?

Yes! One group of cyclists took carbohydrate and mineral sports drinks at 39 degrees F. The other group took the same drinks at 97F. Those taking the cooler drinks had lower skin temperature, mean body temperature, and heat storage during a 90-minute ride at 65 percent of their maximum (Vo2 max), and a five percent improvement in their 15-minute all-out race times (Journal of Sports Sciences, September 2010).

Eighty percent of the energy used to power muscles is lost as heat. The harder you exercise, the more heat your muscles produce. A rise in body temperature increases your oxygen requirements. The limiting factor in how fast you can ride over distance is the time it takes to bring oxygen into your muscles, so anything that keeps your body temperature from rising too high will help you ride faster.


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Dear Dr. Mirkin: Why do you recommend eating so many fruits, vegetables, whole grains, beans and nuts?

These foods are loaded with fiber. People who eat the most fiber are at a much lower risk for dying for any reason (Archives of Internal Medicine, published online February 14, 2011).

Fiber is a component in food that cannot be broken down in your intestines, so it cannot be absorbed into your bloodstream. There are two type of fiber: soluble and insoluble. Insoluble fiber helps prevent constipation and may also prevent colon cancer by forming a gel with water to keep stool soft and help it pass from your body.

Soluble fiber helps to prevent and treat diabetes by lowering blood sugar. It binds to water and forms a gel that slows the rate that sugar is absorbed into your bloodstream. It helps to control overweight by binding to other carbohydrates, reducing absorption of calories. It helps to prevent heart attacks by passing into your colon where bacteria convert soluble fiber into short chain fatty acids that are absorbed into your bloodstream. They travel to your liver where they prevent your liver from making cholesterol, lowering blood cholesterol levels.

Plants contain both soluble and insoluble fiber in varying amounts. Good sources of insoluble fiber include whole grains, nuts and many vegetables. Good food sources of soluble fiber include oats, barley, dried peas and beans, and fruits such as plums, apples and citrus. If you eat a wide variety of fruits, vegetables, whole grains, beans and nuts, you will get plenty of both types of fiber.


Recipe of the Week:

New Potato Salad

You'll find lots of recipes and helpful tips in The Good Food Book - it's FREE

February 20th, 2011
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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