Eat more fruits and vegetables—who could argue with that simple advice? Well, amazingly enough, the fruit part is being questionedmostly by advocates of low-carb dietssuch as science writer Gary Taubes and lifestyle guru Tim Ferriss. Some warn that fruit is almost as "evil" as sugar and white bread when it comes to weight gain and overall health.
Fruit and Weight Gain: Guilt by association
What scares some people about fruit is that not only do nearly all of its calories come from carbohydrates, but most of those carbs are sugar, and much of that sugar is fructose. Say fructose and most people think high-fructose corn syrup (HFCS)—our No. 1 sweetener, added to so many soft drinks and processed foods. HFCS is slightly more than half fructose; plain old table sugar (sucrose) is also half fructose, while honey is about 40 percent fructose.
Some recent research suggests that fructose, at least in the large quantities many Americans are now eating and drinking, can have adverse effects on blood cholesterol and triglycerides, worsen blood sugar control, promote abdominal weight gain and pose other health risks (see Wellness Letter, August 2008).
But fresh fruits supply only a small fraction of the fructose Americans consume. You would have to eat several servings of fruit to get as much fructose as in a can of soda.
Moreover, fruits are complicated foods, not just a serving of fructose. Their fiber and other components help slow the absorption of fructose, compared to sugary beverages. Some fruits, such as apples, pears and mangoes, are higher in fructose (and other sugars) and thus calories, but they’re still only moderate sources. Some are relatively high on the glycemic index (a measure of the effect of carbohydrates on blood sugar), but most are moderate. It’s highly unlikely that the fructose in a serving of even very sweet fruit could trigger undesirable effects, such as weight gain.
Fruit juice is another matter, since it contains more sugar and calories per serving, has little fiber and is much less filling than whole fruit. A cup of some fruit juices can naturally contain nearly as much fructose as a can of soda. Thus some (but not all) studies have found that kids who drink lots of fruit juice, like those who drink lots of soda, gain weight and are more likely to be very overweight.
What about studies on fruit and weight gain?
There is no research showing that moderate intake of whole fruits leads to weight gain or undesirable health effects. In fact, studies have found that people who eat lots of fruits and vegetables tend to be thinner and healthier than those who shun them. But that doesn’t necessarily mean that produce is the cause of these good effects. Produce eaters tend to be health-conscious in many ways, and it's hard to tease apart the many factors—even to separate the effects of fruits from those of vegetables. When researchers adjust for factors such as exercise, weight and total calorie intake, the benefits associated with produce seen in studies often weaken or disappear. And when the benefits persist, questions still remain about this "healthy person effect."
Thus, it has been surprisingly hard to prove that fruits and vegetables reduce the risk of heart disease, cancer or obesity (or possibly increase the risk in some people). Here are some recent findings:
- Though only one third of American adults eat fruit two or more times a day, people with healthy weights are much more likely to do so than obese people, according to a CDC report in 2010.
- In a 2009 review paper on fructose, researchers from Tufts University concluded that in order to decrease the high incidence of obesity, diabetes, lipid problems and insulin resistance, people should eat more whole fruits and vegetables and less HFCS and table sugar.
- In a 2010 analysis, researchers from the University of Leicester in England analyzed data from six studies and found that fruit intake had no effect—positive or negative—on diabetes risk.
- In the past year Danish, Portuguese and Dutch studies linked high fruit intake to a decreased risk of heart attacks. However, in a study of Italian women, fruit intake seemed to have no effect on the risk of heart disease.
- The effects of fruit on weight, heart disease and diabetes have not been thoroughly studied, according to a French review paper in 2009. And though fruit consumption has been linked to reductions in blood pressure, prevention trials looking at the effect of fruits on heart health haven’t shown a clear benefit.
- A review paper last year in Nutrition noted that whole fruits don’t have the same adverse metabolic effects as fructose (usually from HFCS) added to processed foods—probably because of their fiber and antioxidants.
Bottom Line: Fruits are a key part of a healthy, balanced diet. They are low to moderate in calories (usually 40 to 100 calories per serving), and most are rich in vitamins, minerals (notably potassium) and other potentially beneficial compounds such as carotenoids and flavonoids. Thanks to their fiber and high water content, they’re filling. And they’re an easy snack that needs no cooking—portable and sweet (but lower-calorie) substitutes for sugary snacks. Whole fruits are a much better choice than juice; most people should limit themselves to one cup of fruit juice a day.
Originally published in The University of California, Berkeley Wellness Letter (July 2011)