The Importance of Vegetables

Out of all the foods we could potentially eat, vegetables and fruit are some of the only items not mired in controversy: virtually every health authority agrees they should have a place at the table (literally!). In fact, the greatest common denominator among all diets that have a scientific support for their health-promoting claims is high-vegetable intake. This goes for the Paleo diet, the Mediterranean diet, plant-based diets, and indigenous diets from around the world. The body of evidence supporting high intakes of fresh, fibrous, low-energy-density plant foods is truly staggering.

Across the globe, “Blue Zone” areas (which boast a high concentration of centenarians, and are frequently studied for longevity clues) are characterized first and foremost by their emphasis on vegetables. The Okinawans consume a famously vegetable-rich diet that includes mineral-rich gourds, bittermelon, local herbs and greens, and sweet potatoes. In Costa Rica, residents of the Nicoya Peninsula region (another longevity hotspot) consume abundant garden vegetables, squash, and tropical fruit (especially mangoes, papaya, and oranges). People living on the Greek island of Ikaria eat diets rich in fresh, organic produce and herbs (often grown and picked from their family gardens). The veggie-abundant, high-micronutrient pattern continues for other centenarian-filled areas like Sardinia, Italy; Acciaroli, Italy; and Loma Linda, California. (Although Blue Zone diets are often described as plant-based, we should keep in mind that none of them are vegan, and only one community—the Seventh-Day Adventists of Loma Linda—is vegetarian.)

High vegetable intake is also a hallmark of hunter-gatherer diets. Even the Inuit go to great lengths to collect nutrient-dense plant foods that provide a wide spectrum of micronutrients, prebiotics, and probiotics not available from meat and fish (including chlorophyll-rich seaweeds, berries, mosses, wild leafy greens, tubers, and the partially digested stomach contents of animals).

Of course, the value of vegetables has been confirmed in more than just studies of homogenous populations (Blue Zone residents also partake in other health-promoting diet and lifestyle practices, which makes it hard to tease out the effect of vegetables alone). Study after study shows that higher vegetable consumption (at least five to eight servings a day) reduces the risk of disease, everything from diabetes to osteoporosis to diseases of the gastrointestinal tract to cardiovascular disease to autoimmune diseases to cancer. There are three likely reasons. First, vegetables tend to be rich in very important vitamins and minerals, including the most absorbable form of calcium (see Why Don’t I Need to Worry About Calcium?). Second, vegetables contain plenty of fiber to support a healthy diversity of gut microorganisms (see The Fiber Manifesto Part 1 of 5: What Is Fiber and Why Is it Good?). Third, vegetables are rich in thousands of different beneficial plant phytochemicals. Recall that phytochemicals abound in antioxidant, anti-inflammatory, and other health-promoting properties (see The Amazing World of Plant Phytochemicals: Why a diet rich in veggies is so important!). All of these components add up to serious benefits for people who include abundant vegetables in their diets.

 

Benefits of High-Veggie Intake

When we look at the statistical relationships between vegetable consumption and mortality or disease risk, it becomes clear that the more vegetables we eat, the more protected we are. For every serving of vegetables or fruit we consume, we reduce the risk of all-cause mortality (a measurement of overall health and longevity) by 5 percent, with the greatest risk reduction seen with 8 servings per day and more. That means that eating eight servings of vegetables and fruits per day needs to be seen as a bare minimum for supporting health. It also means that the more we’re able to increase our vegetable intake, the more benefits we’ll see reflected in our health.

Even more exciting, those benefits extend to virtually every chronic disease afflicting modern society. For example, vegetables can be protective against all the following conditions:

Diabetes: Vegetables help reduce diabetes risk through a number of mechanisms, including supplying micronutrients necessary for blood sugar regulation, helping reduce the glycemic load of a meal, and containing fiber to slow down glucose absorption. Vegetables can also reduce risk factors for diabetes by decreasing the energy density of the diet and encouraging weight loss (abdominal fat, especially around the organs, is a major contributor to diabetes in people who are genetically susceptible). Not surprisingly, vegetable intake has frequently been associated with lower diabetes risk, with one meta-analysis finding that each 0.2 serving per day increase of green leafy vegetable intake was associated with a 13% lower risk of type 2 diabetes (yes, even one-fifth of a serving was able to lower diabetes risk that profoundly!).

Cardiovascular disease: Vegetables can have an extremely protective effect on the cardiovascular system by promoting healthy blood pressure (due to their abundance of potassium, calcium, and magnesium), reducing oxidative stress (due to their antioxidants), encouraging healthy body fat levels (by reducing the energy density of the diet and supporting weight loss), reducing LDL levels (through the actions of fiber binding to cholesterol in the intestines), and containing many micronutrients needed for vascular health. One study found that among a cohort of over 13,000 women, those consuming the most vegetables had a 38% reduced risk of dying from cardiovascular disease compared to women eating the fewest vegetables.

Autoimmune disease: Vegetables supply key nutrients for immune function, while also providing multiple forms of fiber to boost gut health (and consequently protecting against leaky gut, a precursor for autoimmunity). (The one caveat here is nightshade vegetables, which, despite being nutrient-dense, also contain compounds that can aggravate autoimmunity, see The WHYs behind the Autoimmune Protocol: Nightshades)

Osteoporosis: Vegetables supply an assortment of nutrients needed for bone health, including calcium, magnesium, phosphorus, chromium, and vitamin K (berries have also been linked to higher bone density, potentially due to some of their phytochemicals and antioxidants). Among postmenopausal women, one study found that every 100g increase in vegetable and fruit intake was associated with a 0.0062 g/cm2 increase in bone mineral density at the whole body, 0.0098 g/cm2 increase at the lumbar spine, and 0.0060 increase at the total hip. In fact, additional studies show that high vegetable consumption is far better correlated with bone health than dairy consumption.

Cancer: The anti-cancer properties of many plant phytochemicals have been well documented. In addition, the chlorophyll found in plant foods can help mitigate the potentially carcinogenic properties of heme iron (the form of iron abundant in red meat), and certain fibers in vegetables and other plant foods appear protective against colorectal cancer. See The Link Between Meat and Cancer.

Obesity: Along with helping avoid micronutrient deficiencies associated with obesity, vegetables are the lowest energy-density foods in existence, adding bulk (fiber and water) to any meal and reducing the overall energy density of the meals we eat. This helps us naturally lower our caloric intake and makes it easier to reach a healthy body weight (especially because vegetables can also displace more obesogenic foods that combine concentrated fats, carbohydrates/sugar, and salt in ways that encourage overeating). See Healthy Weight Loss with Paleo, Part 1: Modifying Dietary Choices to Support Fat Metabolism.

Clearly, there are many, many important roles vegetables and fruit play in supporting our health. Vitamins, minerals, fiber, and an astounding spectrum of phytonutrients are packed into these fabulous plant foods! Hence why they’re a major component of the Paleo diet, and should take up a large visual portion of each meal we eat. In fact, with two-thirds to three-quarters of every plate covered in vegetables and fruit, the Paleo template could be considered a plant-based diet. (See The Diet We’re Meant to Eat, Part 3: How Much Meat versus Veggies?, The Fiber Manifesto;Part 1 of 5: What Is Fiber and Why Is it Good? , and The Amazing World of Plant Phytochemicals: Why a diet rich in veggies is so important!).

 

Key Nutrients in Veggies

Vegetables and fruit supply key vitamins and minerals as well as phytochemicals and fiber (see The Fiber Manifesto;Part 1 of 5: What Is Fiber and Why Is it Good?  and The Amazing World of Plant Phytochemicals: Why a diet rich in veggies is so important!). Although some of these nutrients are available in specific animal foods as well, plants tend to be the richest sources (see The Diet We’re Meant to Eat, Part 3: How Much Meat versus Veggies?). Let’s review some of the amazing nutrients vegetables and fruit have to offer us that are either limited in or that we just can’t get from animal foods.

Carotenoids (including vitamin A, lycopene, and beta-carotene): These are potent antioxidants and important for immune system function. Vegetables and fruits rich in carotenoids include: anything red, orange, or yellow (like carrots, beets, squash, sweet potato, cantaloupe, apricots, mangoes, and bell peppers) and also dark green (like kale, spinach, collard greens, and broccoli). Tomatoes are particularly rich in lycopene.

Diallyl Sulfide: A compound created and released by crushing garlic and other alliums (its precursor is allicin). It has potent antimicrobial effects (including acting against the stomach ulcer bacteria H. pylori), reduces risk of cardiovascular disease, and may be responsible for the protective effect that garlic has against colorectal cancer. Foods containing diallyl sulfide include garlic, onions, chives, shallots, scallions, and leeks.

Dithiolethiones: A class of cancer-protective compounds that also induce detoxification. Sources of dithiolethiones include cruciferous vegetables such as broccoli, collard greens, kale, and cabbage.

Polyphenols: A class of chemical compounds with antioxidant properties, helping prevent cell damage from free radicals and potentially reducing the risk of heart disease and other chronic diseases. Rich sources include berries, citrus fruits, brightly colored vegetables, dark chocolate, and plums. See Polyphenols: Magic Bullet or Health Hype?

Plant Sterols and Stanols: With a similar chemical structure to animal cholesterol, these compounds can block the absorption of cholesterol in the small intestine and reduce levels of LDL (“bad”) cholesterol in the blood without altering levels of HDL (“good”) cholesterol. Sources of plant sterols and stanols include nuts, legumes, and most fruits and vegetables.

Flavonoids: A class of more than 6,000 compounds with a range of health benefits, including reducing inflammation, protecting against smoking-related cancers, and reducing cardiovascular disease risk. They also have antibacterial properties. Foods rich in flavonoids include parsley, berries (especially blueberries), citrus fruits, and cocoa.

Isothiocyanates and Indoles: Sulfur-containing plant chemicals with strong anticancer properties due to their ability to help suppress tumor formation and eliminate carcinogens from the body. Foods with isothiocyanates and indoles include cruciferous vegetables such as broccoli, cabbage, cauliflower, kale, and Brussels sprouts, especially when eaten raw.

B Vitamins: These vitamins are important in cell metabolism (including cell growth and division), immune system function, and nervous system function. Vegetables and fruits rich in B vitamins include: orange and red vegetables (like carrots, sweet potatoes, and beets), grapefruit, peaches, oranges, watermelon, bananas, many green vegetables (like artichoke, asparagus, okra, broccoli, and green pepper), green leafy vegetables, and mushrooms, and cauliflower. Avocado is also very high in several B vitamins.

Vitamin C: Vitamin C serves as a potent antioxidant, is necessary for immune system function, and is also necessary for several enzymes to function in the body (like some enzymes that help make collagen, which is why vitamin C deficiency causes scurvy). Vegetables and fruits rich in vitamin C include: oranges, grapefruit, kiwi, berries, papayas, lemons, pineapple, lime, artichoke, asparagus, avocado, broccoli, carrots, cauliflower, cucumber, green pepper, kale, mushrooms, onions, potatoes, spinach, squash, and sweet potato.

Vitamin K: Vitamin K is critical for making some important proteins in our body that are involved in blood clotting and metabolism. Vitamin K is found in cruciferous vegetables (broccoli, cauliflower, cabbage, kale, Brussels sprouts, turnip greens) and also dark green leafy vegetables.

Calcium: In addition to forming bone, calcium is essential to many processes within the cell, as well as neurotransmitter release and muscle contraction (including our hearts beating!). There’s some research to suggest that the calcium from vegetables is much more readily absorbed and used by our bodies than the calcium in dairy, likely one reason why high vegetable consumption protects against osteoporosis and hip fracture in the elderly. Vegetables and fruit rich in calcium include dark green vegetables, parsnips, papaya, kumquats, black currants, rhubarb, oranges, tangerines, figs, turnips, and butternut squash. Calcium is also found in nuts and seeds, especially sesame seeds.

Chromium: Chromium is important for sugar and fat metabolism. Vegetable and fruit sources of chromium include: broccoli, tomatoes, apples, bananas, onions, garlic, cabbage, carrots, mushrooms, parsnips, and green leafy vegetables.

Copper: Copper is involved in the absorption, storage, and metabolism of iron and the formation of red blood cells. Vegetables and fruit containing copper include: artichokes, avocados, pineapple, plums, dates, kiwis, litchis, cherries, parsnips, pumpkin, winter squash, and green leafy vegetables.

Magnesium: Magnesium is necessary for cells to live. Over 300 different enzymes within our cells need magnesium to work, including every enzyme that uses or synthesizes ATP (the basic energy molecule in a cell) and including enzymes that synthesize DNA and RNA. Vegetables and fruit rich in magnesium include all green vegetables, berries, passion fruit, bananas, carrots, squash, sweet potatoes, and especially dark green leafy vegetables like spinach and kale.

Manganese: Manganese is necessary for enzymes that work to protect the body from and repair damage caused by free radicals. Vegetables and fruits high in manganese include sweet potatoes, raspberries, pineapple, grapes, kiwis, figs, bananas, leeks, eggplant, beets, cruciferous vegetables (broccoli, cauliflower, cabbage, kale, Brussels sprouts, turnip greens), and dark green leafy vegetables.

Potassium: Potassium is critical for the function of every cell; it is necessary for nerve function, cardiac function, and muscle contraction. Vegetables and fruit rich in potassium include cruciferous vegetables (broccoli, cauliflower, cabbage, kale, Brussels sprouts, turnip greens), bananas, cantaloupe, avocados, guavas, kiwis, persimmons, apricots, many orange vegetables (carrots, squash, sweet potato), eggplant, and dark green leafy vegetables.

Sulfur: Sulfur is widely used in biochemical processes, including being a component of all proteins and being important for the function of many enzymes and antioxidant molecules. Cruciferous vegetables and vegetables in the onion family are the best sources of sulfur.

Zinc: Zinc is important in nearly every function of the cell, from protein and carbohydrate metabolism to the immune system. Most green vegetables are a good source of zinc, as are pomegranates and avocados.

Fiber: A carbohydrate present in plant cell walls that our bodies can’t digest. It provides us a variety of benefits by:

• feeding beneficial probiotic bacteria in our digestive tracts
• binding with toxins, hormones, bile salts, cholesterol, and other substances in the gut to facilitate elimination
• favorably regulating some hormones (like suppressing the hunger hormone ghrelin, which signals satiety to the brain) and some neurotransmitters (like increasing melatonin, which helps control sleep)
• adding bulk to the stool, which improves the quality of bowel movements

Diets rich in fiber reduce the risk of cardiovascular disease and of many cancers (especially colorectal cancer, but also liver cancer, pancreatic cancer, and others), and promote overall lower inflammation. In fact, the higher your intake of fiber, the lower your inflammation. If you have kidney disease or diabetes, a high-fiber diet reduces your risk of mortality. High fiber intake can even reduce your chances of dying from an infection. Fiber is broadly categorized as soluble or insoluble (that is, whether or not it dissolves in water), and both classes of fiber have different health benefits. In general, foods that are high in fiber include fruit (especially berries), vegetables (especially leafy green vegetables, root vegetables, and cruciferous vegetables), legumes, and nuts and seeds.

Soluble fibers form a gel-like material in the gut and tends to slow the movement of material through the digestive system. Soluble fiber is typically readily fermented by the bacteria in the colon (although not all soluble fibers are fermentable), producing gases and physiologically active by-products (like short-chain fatty acids, which yield a variety of health benefits and vitamins). Soluble fiber also has cholesterol-lowering properties. Rich sources include apples, berries, pears, citrus fruits, and legumes.

Insoluble fiber tends to speed up the movement of material through the digestive system. Fermentable insoluble fibers also produce gases and physiologically active by-products (like short-chain fatty acids and vitamins). Unfermentable insoluble fiber increases stool bulk by absorbing water as it moves through the digestive tract, which is believed to be very beneficial in regulating bowel movements and managing constipation. Insoluble fiber reduces inflammation. It also binds to toxins and surplus hormones in the gastrointestinal tract, facilitating their elimination from the body. Foods high in insoluble fiber include leafy green vegetables, bell peppers, cruciferous vegetables (such as broccoli, bok choy, cauliflower, and Brussels sprouts), celery, and carrots.

Lignans: A type of polyphenol-rich fiber that can be metabolized by intestinal bacteria into enterodiol and enterolactone, which may play a role in preventing osteoporosis, cardiovascular disease, and hormone-associated cancers (breast, endometrial, ovarian, and prostate). Foods high in lignans include flaxseeds, sesame seeds, legumes, and cruciferous vegetables.

As we can see, some vegetables and fruits are little powerhouses of nutrition (like kale), but in order to make sure we get adequate amounts of all the necessary vitamins and minerals, eating a wide variety is key. Also keep in mind that often vitamins are linked to the color of a vegetable or fruit, so “eating from the rainbow” is a good way to ensure nutrient diversity .

Take-Home Message

Eating 8 or more servings of vegetables and fruit per day not only helps us meet important nutritional intake levels of vitamins, minerals and fiber (see How many carbs should you eat?), it’s also definitely an achievable goal.  That means choosing 2 or 3 servings of vegetables at every meal (yes, even breakfast). How much is a serving? The standard vegetable and fruit serving size established by the World Health Organization in 2005, and used in more scientific studies evaluating benefits of high vegetable and fruit consumption, is defined as 80 grams raw, or just shy of 3 ounces.

This roughly translates to:

• 1 cup raw vegetables
• ½ cup cooked vegetables
• 2 cups raw leafy greens
• 1 medium fruit (about the size of baseball)
• ½ cup chopped fruit (or berries)
• ½ cup cooked fruit

If you’re concerned with getting enough veggies in, spending a few days measuring your vegetable servings to keep yourself on track is a great way to increase awareness of your vegetable intake and whether or not it meets your goals.  The most intuitive way to get enough veggies into our diets is to structure each plate so that between 2/3 and 3/4 of it is covered with vegetables and fruit (see Carbs Vs. Protein Vs. Fat: Insight from Hunter-Gatherers and The Diet We’re Meant to Eat, Part 3: How Much Meat versus Veggies?) with the remaining 1/4 to 1/3 being high-quality meat or seafood.

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