Do we need vegetables in our diet? » Diagnosis: Diet

Vegetables » Diagnosis: Diet

Do we need vegetables in our diet?

As outrageous as this may sound, I find no scientific evidence that vegetables are essential components of the human diet, because I am not aware of a single study that compares a diet containing vegetables to a diet without vegetables.

Thankfully, scientific laboratories are not our only sources of valuable information about the world. There’s real life evidence we can turn to that can answer our question.

We happen to know that a number of populations throughout history have eaten diets containing extremely few or even no vegetables, and historical reports tell us that these people were very healthy. Eskimo populations at the turn of the 20th Century are the clearest examples of this phenomenon. Nothing grows up there, so these frozen folks had no choice but to eat an essentially all-animal diet. Physician explorers of the time (before trade routes exposed traditional peoples to outside foods) observed that cancer was virtually nonexistent in Eskimo villages. Even if the historical record doesn’t prompt you to wonder whether vegetables are really necessary in the fight against cancer, it should at least convince you that vegetables are not required in the human diet for daily bodily function.

That these people were somehow able to get all of their essential vitamins and minerals entirely from animal foods I find to be fascinating and important information. These were not short-term studies lasting weeks or months or a couple of years. These were real people living entire lifetimes, being physically active, reproducing, etc., with little to no vegetable matter in their diet (and therefore virtually no carbohydrate). No biased researchers, no study subjects guessing about what they ate or cheating on their diets. I would argue that this kind of evidence is far more convincing than any scientific study.

Are vegetables good for us?

Okay, so they don’t seem to be necessary, but how do we know that Eskimos wouldn’t have been even healthier if they had added vegetables to their all-meat diet? We don’t know. So let’s look at the scientific research to see what it tells us about vegetables and health.
The reason why we are led to believe that vegetables are good for us is that there are thousands of epidemiological studies comparing high-vegetable diets to low-vegetable diets, and often (but not always), the people eating high-vegetable diets seem healthier. So why isn’t that convincing? Because when epidemiologists compare two different diets, there are usually LOTS of differences between those two diets, not just the amount of vegetable consumed.
For example, because people believe vegetables are healthy, people who eat more vegetables tend to be more health-conscious in general. However, health-conscious people also tend to do lots of other things differently from the average person—they may eat less processed food, drink less alcohol, smoke less, eat less sugar, count calories, exercise more, etc. These other differences are very hard to account for in studies. The only way to really figure out if vegetables are healthy is to compare a diet with vegetables to a diet without vegetables. I know of no scientific study that has done this.
So, epidemiological studies suggest that people who eat more vegetables might be healthier. In order to prove this hypothesis, we need to do experiments. What do actual clinical experiments tell us?
I compiled the following information for a recent presentation I gave at the Ancestral Health Symposium:
As of this writing (August 2012), there are 762 clinical studies listed in PubMed (a scientific search engine) having to do with vegetables and human health. Most of these are studies of how to get people to eat more vegetables; there are very few clinical trials attempting to show that vegetables are healthy. There were only 38 clinical studies designed to evaluate specific health effects of actual vegetables (as opposed to special concentrated vegetable extracts or isolated vegetable nutrients), and the vast majority of these (31 of the 38), unfortunately, used fruits and vegetables, instead of just vegetables. Fruits are so different from vegetables that it’s like comparing apples and oranges…except that it’s even worse, because at least apples and oranges are both fruits! However, let’s try to ignore these major design flaws and see what researchers found.
18 of these 38 clinical studies were “negative”, meaning the researchers did not find the health benefit they were looking for.  The remaining 20 studies were “positive”, meaning researchers found a health benefit when they compared groups of people who ate more (fruits and) vegetables to those who ate less of these foods.
20 positive studies is nothing to sneeze at, so at first glance, one might think that eating more (fruits and) vegetables might be a good idea. However, upon closer scrutiny, flaws become obvious that make it impossible, unfortunately, to know whether the results are actually due to the (fruits and) vegetables and not to some other factor.
Of the 20 “positive” studies, 10 did not take refined carbohydrate into consideration. This means that the group of people who ate more (fruits and) vegetables might have been healthier because they were eating less refined carbohydrate than the group that ate fewer vegetables.
The remaining 10 “positive” studies did not simply increase the amount of (fruits and) vegetables people ate; they also changed other aspects of lifestyle, such as fat consumption, alcohol intake, smoking, exercise, salt use, and/or refined carbohydrate intake. Therefore, we do not know whether the people who ate more (fruits and) vegetables were healthier because of the vegetables or because of some other aspect of the intervention.
Oh, and In case you’re wondering, of the 7 lonely studies that did look only at vegetables (instead of fruits and vegetables together), 6 of those 7 studies just happened to fall into the negative category, meaning that the vegetable(s) did not provide the health benefit expected. Hmmm.
So, we don’t have any clear scientific proof yet that vegetables are healthy for us. However, just because scientists have not yet conducted the kinds of studies that can tell us whether vegetables are healthy does not mean that they are not good for us; it just means that the idea that vegetables are good for us remains an unproven hypothesis.

Don’t we need to eat vegetables for fiber?  

Fiber is an important enough topic that I gave it its own page on the site.

Aren’t vegetarians healthier than other people?

For detailed information about this question, please see vegetarian diets and vegan diets.  

Aren’t vegetables important sources of vitamins and minerals?

Below is a copy of a PowerPoint slide I prepared for a presentation at the 2012 Ancestral Health Symposium entitled “Little Shop of Horrors: the risks and benefits of eating plants.” In this slide you can see that animal products are superior sources of most essential vitamins and minerals, including 4 that do not exist in plant foods at all:

Aren’t vegetable antioxidants important for health?

This is a very complicated topic, and I’ll be writing lots more about this over time. For starters, many vegetable antioxidants that appear to have anti-cancer and anti-inflammatory properties in laboratory studies also happen to be the same chemical weapons that plants use to defend themselves.  Therefore, it makes sense that many of these isolated compounds not only have the power to kill cancer cells, they also have the power to kill healthy, normal cells. Like any form of chemotherapy, the most powerful vegetable antioxidants are, at best, double-edged swords.
Since antioxidants from each vegetable family are numerous, unique and complex, they will be explored in detail in the special occasional articles in my food blog. From cruciferous vegetables like broccoli to nightshades like white potato, you will discover the clever ways in which each vegetable family protects itself in the world, and how its specialized defensive chemicals affect your body.
The first Veggie blog post feature is already available:  Click HERE to read “Is Broccoli Good for You? Meet the Crucifer Family.”
The second Veggie blog post feature is now available:  Click HERE to read “How Deadly Are Nightshades?”, which includes lots of interesting information about potatoes, as well as about tomatoes and eggplants (which are actually fruits masquerading as vegetables).

Bottom Line about Vegetables

There is no scientific evidence proving that vegetables are necessary, let alone good for us.  However, most vegetables are naturally filling, low in carbohydrate, and low in calories, and therefore may be useful alternatives to junk food, sweets, baked goods, dairy products, and seed foods (grains, beans, nuts and seeds) when trying to control weight. Very sweet and starchy high glycemic index vegetables, such as white potatoes and beets, are exceptions to this rule.
Due to high fiber content, vegetables can be hard to digest, especially if eaten raw.
Vegetable nutrients are harder for us to absorb and use than animal food nutrients.
Vegetables contain naturally-occurring defensive chemicals that are designed to harm creatures that try to feast upon them.  These chemicals are very toxic to living cells, however, the concentrations that exist in most types of whole vegetables may be relatively safe for most people to eat in moderation.  Vegetable extracts and concentrates may not be as safe as whole vegetables because the “dose” of vegetable chemicals is much higher in these products. Some vegetable families contain more potent toxins than others, so watch my food blog for my “Vegetable of the Month” feature to learn which vegetables are most likely to cause trouble for sensitive people.
Some vegetables are actually fruits, because they contain seeds.  Examples of fruits masquerading as vegetables include:  cucumbers, tomatoes, eggplant, and squashes. Pureed preparations of these “vegetables” which include pureed seeds are probably riskier choices, as seeds contain especially harmful chemicals that are released when seeds are pureed.
Some vegetables are actually legumes.  Examples include green beans, wax beans, and snow peas.  The pods or beans inside of these vegetables pose special risks to our health.  For more information, see the grains/beans/nuts/seeds page.
Young vegetable sprouts contain higher concentrations of potentially harmful chemicals than mature vegetables because baby plants are vulnerable and need more protection from predators.
As a general rule, toxins are more likely to be concentrated in the skins of vegetables, to protect the plant on its outer surface.  Sensitive individuals may therefore want to skin vegetables before eating. Cooking can also reduce the activity of some of these chemicals.
We and most of our ancestors have been eating vegetables for as long as 2 million years, so our bodies have adapted some ways of handling their natural toxins that may reduce their risk to our health.  This is probably not true of “newer” foods, such as seed foods (5,000 to 10,000 years), refined carbohydrates (100-150 years), and artificial food additives (about 70 years).  Therefore, vegetables are likely to be superior choices when compared to these newer foods.