We've all heard it — from our parents, from our peers, from the news media, even from movie heroes. It is repeated like a mantra until it is accepted as fact without question:
"Eat your vegetables. They're good for you."Let me be clear about this up front: Vegetables are good for you. They contain vitamins, minerals, and fiber. They have some other long-term health benefits that cannot be obtained from any other food source. If you like vegetables, then by all means keep eating them.
But if you're like me, and you don't like vegetables, are they really the miraculous life-giving Food of the Gods they're made out to be? Are they really so good for you that you need to endure the hardship of putting these foul plants in your mouth just to stay healthy? Do the benefits of eating vegetables outweigh the terrible cost of having to eat them?
I'm here to say: no. My main thesis is this:
There is insufficient evidence that vegetables are necessary for healthy living, provided you get enough vitamins, minerals, and fiber from other sources.In other words, if you're getting enough vitamins, minerals, and fiber from non-vegetable sources, the remaining health benefits of vegetables are marginal — and if you don't like vegetables, the health benefits you'd gain are marginal enough that it's not worth learning to like them.
The notion that vegetables are "good for you" evolved at a time when our ancient ancestors had no other source of vitamins. If you didn't eat vegetables (or fruits) with vitamin C in them, you would get scurvy. The people of the time didn't know it was the vitamin C in the vegetables and fruits doing this, they simply knew that not eating vegetables or fruits meant scurvy. Similarly, if you didn't eat yellow vegetables, you would get night blindness from vitamin A deficiency. You could also get beriberi from insufficient thiamine (vitamin B1) and pellagra from insufficient niacin (vitamin B3). In the olden days, eating your vegetables really could spell the difference between life and death, because we didn't know what it was in the vegetables that gave them such great powers of health preservation.
But this isn't the olden days any more. Now we do know what was in the vegetables that gave them their powers of disease prevention. And, as a result, we have multivitamin pills now. Getting enough of the nutrients that vegetables traditionally provided can be accomplished by taking a One-A-Day™ tablet in the morning.
Minerals are similar. If you don't get enough iron, for example, you can get hypoferremia. (Conversely, if you get too much iron, it can damage your liver. Vitamin A in the form of retinol is similar; get too much and you'll get hypervitaminosis A, which has a whole array of unpleasant symptoms.) If you don't get enough potassium, your muscles won't work right. If you don't get enough magnesium, it can interfere with your nervous system. And there are other minerals just as important as these. While it's true that various vegetables do contain various minerals, it's also true that nearly every broad-spectrum multivitamin supplement on the market is also a multimineral supplement.
Dietary fiber — soluble and insoluble, viscous and nonviscous — is good for you. It can have a probiotic effect on your gut flora, it can help to clean things out of your intestines, and in some cases it can even pull a little bit of cholesterol out of you (or, rather, pull out some bile salts, which your body synthesizes from cholesterol) and reduce the rate at which starches and sugars are absorbed.
Vegetables have fiber.
But vegetables aren't the only source of fiber out there. Whole wheat bread and pasta, if you like such things, also have some insoluble fiber in them. Oats and particularly oat bran have viscous soluble fiber in the form of β-glucans. Psyllium husk is practically made of viscous soluble fiber. And of course, there are many kinds of fruit that contain fiber as well.
There are a few things some vegetables have which are not available in supplement form, which have established health benefits. These benefits, however, ane not very strong. Even today, most of them are still in the "may help with" or "probably helps prevent" category.
According to Annals of Internal Medicine, there's no evidence that vitamin supplements reduce the risk of either cardiovascular disease or any kind of cancer.
But according to these studies used by the Diet and Cancer Report, non-starchy vegetables do reduce the incidence of certain kinds of cancer. Unfortunately, most of the studies involved were case-control studies; according to the Harvard School of Public Health, case-control studies can have skewed results and are generally less reliable than cohort studies. There aren't many cohort studies on the Diet & Cancer Report page, and the few that are there don't tell a very convincing story. The report on non-starchy vegetables and stomach cancer, for instance, gives an average relative risk of 0.98, meaning there was almost no measurable effect at all. (And you'll notice that the error bars on that page all overlap the 1.0 line.)
According to this Oregon State University news release, the glucosinolates in cruciferous vegetables "may reduce the risk of prostate, breast, lung and colorectal cancer." But, these glucosinolates can only be absorbed when eaten in conjunction with myrosinase, an enzyme not found in glucosinolates but present in these vegetables when they haven't been cooked very long.
As stated above, vitamin supplements have not been shown to reduce the risk of cardiovascular disease.
But according to the Nurses' Health Study, a high fruit and vegetable intake reduces the risk of heart attack and stroke by about 30%. (Was it the fruit? Or the fiber? Or the phytochemicals in the vegetables? The study didn't distinguish. It's suggestive of a protective effect from vegetables, but not conclusive.)
According to an article in The Journal of Nutrition, Health, and Aging, increased vegetable intake is associated with a reduced risk of dementia and slower cognitive decline in old age. However, increased fruit intake isn't. This implies that it's not the vitamins or fiber in the vegetables that's making the difference, since fruits have both.
According to an article in Neurology, which studied 8085 patients age 65 and over, the risk of getting any form of dementia among the patients who ate fruits and vegetables every day was only 72% of the risk of getting dementia among the patients who didn't. (Omega-3 fatty acids, like those in fish, were also associated with a reduced risk of dementa, but omega-6 fatty acids were associated with an increased risk of dementia among subjects that didn't have the ApoE ε4 gene.) But pay attention to those error bars. Although the measured relative risk in this study was 0.72, the 95% Confidence Interval for that relative risk ran all the way from 0.53 to 0.97. This means that, with 95% confidence, the risk of dementia among patients who eat fruits and vegetables could be as high as 97% of the risk among patients who don't.
Finally, according to this article in the American Journal of Clinical Nutrition, certain mechanisms of fruit and vegetable phytochemicals have been studied and "can have complementary and overlapping mechanisms of action, including modulation of detoxification enzymes, stimulation of the immune system, reduction of platelet aggregation, modulation of cholesterol synthesis and hormone metabolism, reduction of blood pressure, and antioxidant, antibacterial, and antiviral effects." Only some of these "can haves" have been actually studied in humans.
Again, if you like vegetables, then by all means eat them. They're good for you. But if you don't like vegetables, you're probably not going to be driven to an early grave if you don't eat them, provided you keep your weight in a healthy range and get at least semi-regular exercise. (And take any supplements you need to avoid vitamin and mineral deficiency. But really, you don't need a lot of 'em.)
A lack of vegetable intake correlates to some degree with obesity. (c.f., for example, Relationship of fruit and vegetable intake with adiposity: a systematic review, published in Obesity Reviews.) One possible reason is that most vegetables contain a good deal of soluble fiber, which absorbs water and moves very slowly through the digestive tract. This creates "bulk" and gives the sensation of being fuller longer, thus reducing your appetite.
So then, what if you don't like vegetables, and you're overweight?
Well, no program of weight loss is going to be easy. When it comes to curbing your appetite, there are a bazillion little tricks that work for some people but not others. There are no miracle weight-loss gimmicks. And there's no guarantee that forcing yourself to add (yicch) vegetables to your diet is going to help you lose weight.
You'll note that, of the studies used in the Diet and Cancer Report linked above, only one deals with colon cancer, and it only looks at the effect of garlic. What happened to the link between vegetables and a reduced instance of colon cancer, which was discussed so often in the 1990s?
Early studies found what appeared to be a strong negative association between eating fruits and vegetables and getting all kinds of cancer. But there were problems with these early studies, as shown on this page at the Harvard School of Public Health. One promising avenue, for a while, was to focus on the differences between vegetable fiber and whole grain cereal fiber. Some of these early studies focused on on colon cancer, and showed a reduced instance of colon cancer among people who consume vegetable fiber. Similar studies using cereal fiber did not show a reduced instance of colon cancer. (Source: http://www.vegetarian-nutrition.info/vn/fiber_colon_cancer.php.) This sounded pretty convincing, and media reports quickly trumpeted this as a "win" for vegetables.
But as with so many other cases of media reporting on science, however, this veggie victory was premature. According to this article from April 2000, two large studies in the New England Journal of Medicine failed to find any correlation one way or the other between the consumption of any kind of dietary fiber, including vegetable fiber, and the incidence of colorectal cancer. A later study in the 8-February-2006 Journal of the American Medical Association confirms this finding. Apparently, eating more vegetables won't make you any less likely to get colon cancer.
Lycopene is a chemical found in tomatoes. It's is an antioxidant — which in the mind of certain trendy nutritional True Believers automatically means that it keeps you healthy, reverses aging, makes you a better lover, and increases your chances of winning the State Lottery. (Of course, there are plenty of other antioxidants out there, including plain old vitamins C and E.) But to convince the fence sitters who wouldn't simply take them at their word, these True Believers presented epidemiological "evidence" that lycopene prevents digestive-tract cancer, prostate cancer, macular degenerative disease, and even lung cancer and skin cancer.
The epidemiological evidence for lycopene consisted of things like "Italians eat lots of marinara sauce, and they have a lower incidence of cancer of the digestive tract." This is true. But Italians also eat a lot of olive oil and garlic. Maybe olive oil and garlic protect against digestive-tract cancer. Italians also have a higher incidence of membership in the Mafia. Maybe being in the Mafia protects against digestive-tract cancer. Concluding that lycopene is responsible for Italians getting less digestive-tract cancer is like concluding that punk-rock haircuts are responsible for swearing. Correlation, especially when so many other factors are involved, does not imply causation.
Next chapter: Why the Push for Vegetables?
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