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Caffeine: Good When You Exercise, Bad When You Rest

Caffeine increases sugar absorption from the gut. Taking caffeine when you eat carbohydrate-containing foods can double your rise in blood sugar (Journal of Caffeine Research, April 16, 2011). Since more than 35 percent of North Americans will become diabetic and have high rises in blood sugar levels after meals, most people should not take caffeinated drinks with meals that contain carbohydrates: bread, spaghetti, or sugared foods and drinks. If you are already diabetic, your blood sugar levels rise even higher and you suffer cell damage. A high rise in blood sugar causes all the horrible side effects of diabetes: blindness, deafness, heart attacks, strokes and so forth. However, during exercise, caffeine can increase endurance (Medicine & Science in Sports & Exercise, July, 2010) by increasing the absorption of sugar from your intestines and by increasing the uptake of sugar by your exercising muscles by as much as 26 percent (Journal of Applied Physiology, June 2006). Caffeine is found in coffee, tea, chocolate, and cocoa.

Sugared drinks cause higher rises in blood sugar than sugared foods.
No solid food is allowed to pass into your intestines. After food enters your stomach, the pyloric sphincter closes. Food is kept in the stomach until it is turned into a liquid soup. Then the stomach muscles squeeze the soup through the pyloric sphincter into the intestines. An orange can be kept in your stomach for up to five hours before it passes into your intestines. Since fruit juice is a liquid, it passes into your intestines immediately. So orange juice causes an immediate high rise in blood sugar, while an orange does not. Studies show that fruits decrease diabetes risk, while fruit juices increase risk (Diabetes Care, July 2008).

Caffeine drives blood sugar levels even higher.
Adding caffeine to sugar in a drink causes blood sugar levels to rise even higher than drinks that have only sugar.

Fruit juice is as damaging as high fructose corn syrup or table sugar.
High Fructose Corn Syrup (HFCS) has been blamed for the ever-increasing rates of obesity and diabetes in North America over the last forty years. However, HFCS appears to be no more damaging than fruit juice or drinks sweetened with table sugar. Most soft drinks are sweetened with HFCS. Both HFCS and conventional sugar (sucrose) contain a mixture of two sugars, glucose and fructose, in nearly the same concentrations: HFCS has 55 percent fructose/42 percent glucose, while sucrose is a 50/50 mixture. These numbers are so close that most researchers feel that the slight increase in the concentration of fructose is not important enough to cause disease in itself. The fructose in orange juice, table sugar and HFCS are equally damaging to your health.

How fructose harms:
Fructose is far more damaging to the liver than glucose and is thought by many physicians to be the main cause of the fatty liver that causes insulin insensitivity and type II diabetes. When your blood sugar rises too high, the pancreas releases large amounts of insulin. Insulin converts sugar to triglycerides. Since high levels of blood triglycerides increase risk for clots, your good HDL cholesterol carries the triglycerides from your blood to your liver to fill up the liver with fat to cause a fatty liver. Fructose causes far higher blood and liver levels of triglycerides than glucose does, so fructose is a more potent cause of a fatty liver. Having a fatty liver prevents the body from responding to insulin and blood sugar levels rise to increase diabetes risk.

During exercise, muscles protect you.
Resting muscles are inactive. They need insulin to remove sugar from your bloodstream. On the other hand, contracting muscles can remove sugar from your bloodstream without even needing insulin (American Journal of Clinical Nutrition, July 2008). The maximum effect is during exercise and continues maximally for up to one hour afterward and disappears at around 17 hours (Journal of Applied Physiology, February 2010).

How caffeine and sugar help you during exercise:
Caffeine increases endurance by helping the body use more sugar from drinks that you take during exercise (Journal of Applied Physiology, June, 2005). The limiting factor to how fast you can move over distance is the time it takes to get oxygen into muscles. Since sugar requires less oxygen than fat or protein do, muscles move faster with more power when they burn sugar. Those who took sugared drinks with caffeine were able to absorb and use 26 percent more of the ingested sugar than those who took the same drinks without caffeine. Caffeine-laced drinks help improve endurance even more in hot weather (International Journal of Sport Nutrition and Exercise Metabolism, February 2011).

You should take caffeinated sugared drinks only when you exercise and for up to an hour after you finish. Taking sugared drinks, with or without caffeine, when you are not exercising causes higher rises in blood sugars that increase risk for diabetes and cell damage.


Dear Dr. Mirkin: What can prevent dementia in older people as they start to forget things? Older people suffering from mild memory and cognition problems are far less likely to progress to Alzheimer's disease if they are treated to protect their blood vessels: for high blood pressure, high triglycerides and cholesterol, low good HDL cholesterol, abdominal obesity, diabetes and heart disease (Neurology, published online April 13, 2011).

In 2004, researchers started to follow 837 people, ages 55 and older, who were forgetful but did not have dementia. More than half had the signs of blood vessel disease listed above. After five years, 35 percent developed Alzheimer's and the majority were from the group who had signs of blood vessel disease. Those with blood vessel disease who received treatment were 40 percent less likely to develop Alzheimer's. Slightly less than ten percent of people with cognitive impairment progress to Alzheimer's each year.

All people, whether they are forgetful or not, should prevent blood vessel disease by getting their bad LDL cholesterol below 100, the diabetic test HBA1C below 5.7, blood pressure below 120/80, triglycerides below 120, and a pinch of their abdominal flesh smaller than one inch. They should exercise every day, lose weight if overweight, avoid refined carbohydrates, sugared drinks and red meat, and eat plenty of fruits, vegetable, whole grains, beans, seeds and nuts. They should also try to get their vitamin D3 level above 75 nmol/L.


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Dear Dr. Mirkin: Do you recommend taking calcium supplements to prevent osteoporosis?

No; taking calcium both with and without vitamin D has been shown to be associated with increased risk for heart attacks and strokes by more than 15 percent (British Journal of Medicine, April 19, 2011). Treating 1000 people with calcium or calcium and vitamin D for five years would cause an additional six heart attacks or strokes and prevent only three fractures.

Calcium supplements increase risk for heart attacks and strokes because they raise blood calcium levels which increases chances of forming clots, a major cause of heart attacks and strokes (J Bone Miner Res, 1997;12:1959-70), thickens neck artery plaques (Atherosclerosis, 2007;194:426-32), calcifies main arteries (J Bone Miner Res, 2010;25:505-12), increases heart attack risk (Am Heart J, 2008;156:556-63) and causes premature death (J Clin Endocrinol Metab, 1996;81:2149-53). Taking calcium without also taking vitamin D increases heart attack risk even further because calcium blocks the activation of vitamin D to cause a relative deficiency of that vitamin.


Recipe of the Week:

Portuguese Potato-Garlic Soup

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

April 24th, 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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