Is Any Amount of Sugar Safe?

Sugar has become a trillion dollar health care problem. But are athletes at risk?

    Photo: Daniel D. Snyder

You can cut down to mid-20th century levels out without reinventing your diet.

It's official. Sugar is killing us—and our economy. With the average American eating 40 teaspoons of the sweet stuff a day, the related health care costs have reached a startling number: $1 trillion. And it's not just limited to the sedentary among us. High-energy lifestyles may not be enough to burn through all this excess carbohydrate.  

Exercise is Protective
There’s an old saying that if the furnace is hot enough, anything will burn, even Big Macs. And for dedicated athletes, there’s truth to the idea. With enough exercise, you can probably prevent almost all of the negative health consequences of sugar.  There are a limited number of studies on the topic, but fit people appear to be generally protected from junk food diets. Even in people who are otherwise overweight, exercise reduces the quantity of liver and visceral fat stored around organs that is associated with the worst health outcomes. 

In a recent study, investigators in the UK asked a group of fit young males to stop training and be as inactive as possible while they intentionally overfed them  with 50 percent extra calories for seven days. Half of the subjects were then assigned to 45 minutes of vigorous treadmill running per day and got additional food to make up for the calories spent exercising 

The inactive overeaters eaters saw their lipids, glucose, and blood pressure all get measurably worse. But these changes were not seen in the group that exercised. The results related to blood sugar regulation were especially striking:

In summary, our study shows that short-term overfeeding combined with reduced physical activity induced a reduction in insulin sensitivity, hyperinsulinemia and altered expression of several key genes within adipose tissue. The addition of daily vigorous-intensity exercise mostly prevented these changes independent of any net effect on energy imbalance. Whether this is facilitated by regular glycogen turnover or some other consequence of muscle contraction per se remains to be explored. These results demonstrate that exercise has a profound effect on physiological function even in the face of a considerable energy surplus.

Exercise is clearly protective. But the interactions aren’t always as clear in the real world as in the lab. A series of new studies have shown that  at least some people may not respond positively to exercise in the way most of us do. For these non-responders to exercise, too much sugar and too many calories may still pose a legitimate threat to health. 

What About Peak Performance?
Exercise may protect your body from some of sugar’s nastiest effects, but when it comes to peak performance, your bodyweight is a key factor. So while the athlete’s furnace may burn hot enough to avoid the medical problems associated with a bad diet, it’s just not hot enough to let us totally ignore what we eat if we want to go fast. 

That said, most of us live in the real world and don’t have the time, energy, or inclination to eat a pristine farm-to-table diet with minimal processed food and no added sugar. And we don’t need to. Sugar consumption has gone up 25 percent since 1980 as it’s insidiously entered everyday foods. You can cut down to mid-20th century levels out without reinventing your diet:

  1. Avoid routine consumption of sugar-sweetened beverages. And avoid drinking sports drinks on training rides or runs shorter than an hour and a half.  Water works fine.
  2. Replace the high sugar snacks at your workplace with fruit.
  3. Read labels. You will be amazed at how much hidden sugar and high fructose corn sweetener there can be in the snacks you munch on. Your morning muffin from Dunkin’ Donuts may pack 49 grams of sugar. And your afternoon granola bar can easily have upwards of 20 grams of sugar. 
  4. Your swell Frappuccino Blended can pack 52 grams of sugar. Go black or ask to see the nutritional information before you order. 
  5. During the holidays or when on vacation, don’t overthink things. Get regular vigorous exercise and you can afford to overeat. 

Michael J. Joyner, M.D., is a physiologist and anesthesiologist at the Mayo Clinic and a leading voice in the world of exercise physiology. Over the past 25-plus years, he's published hundreds of studies, many of which have focused on how humans respond to exercise. Dr. Joyner also writes at Human Limits. The views expressed in his posts are his own and do not reflect those of his employer.

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