Mango Vendor in Bangkok

Several readers have asked lately about the impact of fruit–specifically the sugar in fruit–and it’s capacity to cause weight gain and accelerate aging through insulin signaling:

“Do people usually gain weight because of eating fruit and does the sugar in fruit age us?  I just hate to think that I am doing my body harm by eating fruit.”

If this question sounds insane to you, it shouldn’t. It is actually a very reasonable query that was sparked by two Summer Tomato articles, one about saving money while eating healthy and another on calorie restriction, aging and quality of life. In the first article I recommend thinking of fruit as dessert, a treat to be enjoyed once or twice per day. The second article is about the impact of sugar and calories on aging.

Body Weight

The fact is that fruit contains a lot more sugar than other natural foods and in large enough quantities it can contribute to weight gain. But fruit is certainly not bad for you, nor is it worse for your health than anything else in life.

The sugar in fruit contributes calories to your diet, but since you need calories to survive fruit is still a very good choice. The reason is that in addition to sugar (fructose, to be specific) fruit also has vitamins, minerals, antioxidants, fiber and many other things that contribute to health and possibly slow aging.

On the rare occasions when I do make an effort to lose a little weight, however, remembering that fruit should be dessert is something I keep in the back of my mind. I eat fruit every day, but when trying to lose weight I keep it under two servings and always choose whole fruit–avoiding anything blended or juiced. (Drinking calories is usually a bad idea.)

But this healthstyle tactic is not for everyone.

Why?

Unlike most people trying to lose weight, I already have a very healthy diet and fruit is one of the easiest places I can trim calories without feeling deprived. Cutting out things like fat and protein make dieting very difficult because you are always hungry. In my experience reducing unnecessary carbohydrates–especially sugars–is the easiest and healthiest way to lose weight.

But it is essential to remember most people are not overweight because they eat too much fruit and the vast majority of people would benefit from eating more of it.

Aging

The question about whether sugar causes aging is a fascinating one that I am very interested in.

Yes, in most organisms eating sugar has been shown to promote aging, but this has not been proven in humans. Sugar induces aging via the insulin signaling pathway, so therefore any food that increases insulin signaling could theoretically accelerate aging. The problem is that you need insulin to survive–those who cannot produce insulin have a disease called type 1 diabetes.

The good news is that eating a diet that minimizes insulin signaling is also the best way to lose weight and stay healthy, so if you are living a healthy lifestyle (one that includes fruit) you do not need to worry about anything else.

Although fruits have sugar, it is extremely unlikely that they accelerate aging. In fact, most evidence suggests that fruit slows aging because of its high levels of vitamins, minerals and antioxidants.

If anti-aging is your goal, fruit is your friend not your enemy.

For more on insulin signaling, check out my post at MizFit Online, When is a calorie not a calorie.

Conclusion

While fruits contain sugar, they do not pose a special threat to your health goals. Eat and enjoy fruits as a wonderful and delicious part of life.

How much fruit do you eat?

Originally published August 31, 2009.

For The Love of Food

Welcome to Friday’s For The Love of Food, Summer Tomato’s weekly link roundup.

The interwebs gave us lots of great healthy food tips this week, from an unexpected benefit of eating (and smelling) real, quality food to peeling a mango like a zen master. There is also a great article on DIY packed lunch tips and some good news about beer.

I read many more wonderful articles than I post here each week. If you’d like to see more or just don’t want to wait until Friday, be sure to follow me on Twitter (@summertomato) or the Summer Tomato Facebook fan page. For complete reading lists join me on the social bookmarking sites StumbleUpon and Delicious. I’m very active on all these sites and would love to connect with you there. (Note: If you want a follow back on Twitter introduce yourself with an @ message).

Links of the week

• Confused about nutrition? Eat food! <<Marion Nestle elaborates on her position regarding single nutrient science and why we’re better off just eating food. (Food Politics)
• Complex smells make food more filling <<One of the reasons I emphasize real, high-quality foods on this blog is because they are so much more satisfying and contribute profoundly to a better quality of life. A new study suggests that their wonderful smells may be partially responsible. (New Scientist)
• Another perspective on the sodium wars <<I always love to read Monica Reinagel’s perspective on nutrition trends. Here she elaborates on sodium and high blood pressure. (Nutrition Data)
• Beer for the Bones? <<That’s right. The silicon present in some beers may contribute to bone health. I wouldn’t start drinking more to prevent osteoporosis, but it’s nice to fantasize right? (HealthDay)
• The Zen of Peeling a Mango <<It’s mango season, Mangoes are good and healthy, Easy to peel. (Who doesn’t want to start the weekend with a mango haiku?) (ReadyMade)
• A Butcher’s Tips for Avoiding Cuts in the Kitchen <<Safety first. Playing in the kitchen is fun, but it is easy to hurt yourself. Learn to handle a knife safely from the pros. (Lifehacker)
• 8 Foods That Will Hide Your Bad Breath <<I haven’t written much about Valentine’s Day this year, but a little good breath could never hurt anyone. (Dumb Little Man)
• How to cultivate the packed lunch habit & save <<I’m a big fan of lunch, habits and DIY foods. Saving money doesn’t suck either. This article is full of great tips. (Stone Soup)
• You Know About Insulin. And Now, the REST of the Story . . . <<People LOVE to over-simplify health and nutrition. Insulin gets blamed for a lot, and rightly so, but keep in mind there is a lot more going on than just carbs and insulin spikes. (Diabetic Mediterranean Diet Blog)
• Farro & Winter Vegetables Recipe <<I love Amy. I love seasonal vegetables. And for some reason I’ve never cooked with farro. Something is wrong with this story and I think this recipe solves it. (Cooking With Amy)

What inspired you to eat well this week?

Jeff Miller/University of Wisconsin Madison

Last week The New York Times published a story on the life prolonging effects of a low calorie diet in primates. The study in question found that like other organisms (from yeast to worms to mice), rhesus monkeys that eat 30% fewer calories age more slowly and develop fewer diseases than animals on a traditional diet. Those of us who follow the scientific literature on nutrition and aging are not surprised by this at all.

A few days after the story was published The Times published an op-ed questioning the value of the research. Roger Cohen argues that Canto, the healthier monkey, has suffered tremendously as a result of his restricted diet. He contends that it is far better to be fat and happy (and dead?) than thin and miserable.

To me it seems questionable why Cohen believes Canto is unhappy. If he is making his judgment solely on the image above, I must respectfully disagree with his assessment. To me both monkeys appear relatively miserable.

However, Cohen brings up a crucial question about diet and health. How far are we willing to go–how much are we willing to change our diets–in order to extend our lives?

Quality of life is a very important question.

To me one of the most interesting things about calorie restriction is that life extension is only one of many health benefits. Calorie restriction literally slows down the aging process. As a result the animals subject to a limited diet are able to maintain a high level of physical activity into old age. They are also relatively free of age-related diseases including cancer, heart disease, diabetes and neurodegenerative diseases.

Extended life would arguably not be as desirable if these diseases maintained the same progression as they do in those with normal diets. But freedom from these diseases and preserved physical and mental capacities may indeed be worth some dietary alteration.

The next question is how must the diet be changed?

In the monkey experiment, the calorie-restricted group received 30% fewer calories than the control monkeys, who were allowed to eat what they wanted. It is still unknown if a 30% reduction in calories will extend human life in a similar manner, but short-term experiments have indicated that at least some benefits are immediately apparent when calories are limited, such as lower triglycerides, body fat and blood pressure.

Interestingly, however, there may be alternatives to a strict low calorie diet. Cynthia Kenyon, a scientist at UCSF, was the first to show that the key to the life extending properties of calorie restriction is the insulin signaling pathway. A decrease in insulin signaling slows the aging process and extends life.

In the laboratory, organisms like worms, mice and monkeys always receive a uniform diet that has a consistent effect on insulin signaling. But humans do not eat lab food (at least not usually).

Extensive research over the past several decades has made it clear that different foods impact insulin signaling differently in humans. For example, refined carbohydrates have a large, rapid impact on blood sugar, insulin secretion and insulin signaling. By contrast, fat, protein and fiber have next to zero impact on blood sugar and subsequent insulin signaling.

The implication of the diverse human diet is that we are able to alter insulin levels and signaling in our bodies without undergoing severe calorie restriction. Whether or not a diet that promotes less insulin signaling can slow aging in humans is still unknown, but there are many other benefits associated with a diet that lacks refined carbohydrates.

Insulin signaling is not only tied to the aging process, it is also the primary cause of metabolic syndrome–high triglycerides, insulin resistance, hyperinsulinemia, abdominal obesity, low HDL cholesterol and high blood pressure–as well as type 2 diabetes and heart disease.

A diet that improves these symptoms may or may not slow the aging process directly, but it can certainly promotes a higher quality of life by lowering the risk of many debilitating and life threatening diseases.

Going to farmers markets and eating delicious meals isn’t so bad either.

What are your thoughts on health, diet and quality of life?

Romanesco Broccoli in a Beaker

One of the most consistent themes of nutrition science is that vitamin supplements (pills, powders, liquids, etc.) are almost never able to mimic the beneficial effects of foods that contain the same vitamins. Now new evidence suggests that high doses of these antioxidant supplements–but not whole foods containing them–may actually block the beneficial effects of exercise on insulin sensitivity and metabolism.

Exercise has countless benefits for people of all levels of fitness. One of the most important of these is its ability to improve insulin sensitivity and increase metabolism. For this reason, exercise is considered among the most effective ways to protect against type 2 diabetes.

One of the byproducts of exercise, however, is the production of free radicals that results from the breakdown of oxygen in the muscles. These reactive oxygen molecules can damage cells and DNA, and are implicated in many chronic diseases. Since antioxidants can easily neutralize these reactive oxygen molecules, it has been assumed that antioxidants such as vitamins C and E could only benefit the body.

A new study published in the Proceedings of the National Academy of Sciences suggests that rather than help protect against oxidative damage from exercise, high doses of antioxidant supplements may actually hinder the body’s natural protection against oxidative damage and block exercise-induced metabolic benefits.

In the study, human subjects were given either placebo or 500 mg vitamin C twice per day and 400 IU vitamin E. They were then trained in both cardio and strength training workouts at the gym for 5 consecutive weekdays, 4 weeks in a row. This trial was performed on both previously trained and untrained individuals.

Metabolic rates were tested by blood sample both before the trial and after 1 and 4 weeks of training. Muscle biopsies were taken both before and after the trial for all participants. Several measures of metabolism and insulin sensitivity were measured including plasma glucose concentrations, plasma insulin concentrations, maximal oxygen uptake (VO₂ max), as well as several molecular markers in muscle that are linked to insulin sensitivity and are known to promote the body’s natural defense against oxidative damage.

The researchers found that exercise improved measures of insulin sensitivity in all individuals except those given antioxidant supplements. Also, molecules that protect against oxidative damage are upregulated in response to training, but not when antioxidants are administered.

Previous studies suggest that the body’s natural defenses against oxidative damage require activation by a small amount of reactive oxygen chemicals in the body. These same chemicals have been shown to mediate insulin sensitivity in muscles, and in this study both were shown to be blocked by high antioxidant administration.

The researchers suggest that small doses of reactive oxygen molecules such as the amounts produced by exercise are necessary to induce the body’s natural defense against oxidative damage, and that this process is essential for mediating exercise-induced insulin sensitivity. If this is true it could mean that some (but not all) of the metabolic benefits of exercise could be limited by taking high doses of vitamin supplements. This may be particularly important to individuals at high risk for type 2 diabetes.

Interestingly, foods that contain high levels of these antioxidants have previously been shown to be protective against type 2 diabetes. Although the reason for this is still unknown, the authors suggest the benefit is unlikely due to the antioxidant content of the foods and may depend on other factors.

Even if we do not understand the reason vegetables and fruits are the best source of nutrition, we can still enjoy all their benefits. If you choose to continue taking vitamin supplements, it is advisable to stick to a basic multivitamin that does not contain megadoses of one particular nutrient.

Do you take vitamin supplements? Why? How much do you take?
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