Do you need to eat fruits and vegetables?

What is the role of fruits and vegetables in a healthy diet? Let’s take a closer look at this question.

Eating fruits and vegetables is often recommended to live longer, healthier lives. Observations show that healthy people who eat fruits and vegetables can consistently live into their 90’s and 100’s.¹

While this type of data may show that fruits and veggies can be part of a healthy lifestyle, it doesn’t prove that people live longer specifically because they eat fruits and vegetables.

How many fruits and vegetables do we need to eat? And can we find similar benefits in other foods?

Here’s the current scientific evidence on fruits and vegetables.

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1. What are fruits?

Fruits are the seed-containing portion of various flowering plants. They grow exclusively above ground.

Different types of fruit

The broad categories of fruit include pome, citrus, tropical, melons, stone fruits, and berries. Most fruits taste sweet, although citrus varieties are often sour or bitter. With the exception of bananas, most domesticated fruits are juicy due to their high water content.

Keep in mind that the fruit we have today is not the same as the fruit available to our hunter-gatherer ancestors.²

Nutritional composition of fruits

While fruit does contain fiber, antioxidants, and important vitamins like C, it also contains a fair amount of sugar – around 10% by weight (the rest is mostly water).³ Just taste an orange or a grape. Sweet, right?

Eating whole fruits in moderation – especially ones that are low in sugar, like berries – can absolutely be part of a healthy diet. The soluble fiber in fruit can help with short-term satiety; it also reacts with water in your gut to form a thick gel that helps delay and reduce the amount of sugar absorbed from that fruit. In fact, up to 30% of the sugar from fruit may not be absorbed.⁴

Larger quantities of fruit, however, will deliver a significant sugar load to your intestines. Even if only 70% of that sugar is absorbed, 70% of a big number is still a big number. For example, five servings of fruit per day can be equivalent to the amount of sugar in 16 ounces (500 ml) of soda – 52 grams of sugar!⁵

Low-carb fruits and berries – the best and the worst

Guide What are the best and the worst fruits and berries to eat on a low-carb diet? Here’s the short version: most berries are OK low-carb foods in moderate amounts, but fruits can be seen as candy from nature (they contain quite a lot of sugar).

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2. What are vegetables?

Speaking from a botanical or gardening point of view, vegetables are the leaves, stems or roots of plants. However, many non-sweet fruits are commonly considered vegetables for eating or cooking purposes.

Different types of vegetables

Vegetables can be broadly classified into four categories:

1. Above-ground vegetables: greens (spinach, lettuce, chard, et cetera), cruciferous vegetables (broccoli, brussels sprouts, cabbage, cauliflower, kale, et cetera), bulbs (onions, garlic), and fungi (mushrooms).
2. Below-ground/root/starchy vegetables: beets, carrots, parsnips, rutabagas, turnips, yams, potatoes, sweet potatoes, et cetera.
3. Gourds: pumpkins, hard-shelled squashes, and other winter squashes.
4. Technically fruits but treated like vegetables: avocados, olives, bell peppers, eggplant, tomatoes, and zucchini. Unlike other fruits, these aren’t sweet and are often prepared and consumed with other vegetables. Avocados and olives are unique among fruits and vegetables because most of their calories come from fat rather than sugar or starch.

Nutritional composition of vegetables

Non-starchy vegetables are low-carb and keto-friendly foods that provide 5 or fewer grams of net carbs per 100-gram (3.5-ounce) serving. By contrast, root and starchy vegetables have 6 to 17 grams of net carbs per serving.

Vegetables usually contain moderate to high amounts of fiber, especially avocado — which also happens to be among the lowest in net carbs.

Overall, vegetables are more nutrient-dense than fruits, but their vitamin and mineral content can also be affected by factors like growing and storage conditions. Most veggies are good to excellent sources of potassium, and bell peppers and cruciferous vegetables are also high in vitamin C.

Low-carb vegetables – the best and the worst

Guide What are the best and the worst vegetables to eat on a low-carb diet? Here’s the short version: Vegetables growing above ground are usually low carb and can be eaten freely.

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3. How many fruits and vegetables should people eat per day?

Looking at official recommendations for fruit and vegetable intake in different countries, it’s clear that they’re basically all variations on “5 a day.” The US dietary guidelines, the UK National Health Service, and the World Health Organization all set minimums that are generally equivalent to two cups of fruit and two and a half cups of vegetables each day.

According to the Centers for Disease Control, only 1 in 10 adults consistently meets the US Dietary Guidelines recommendations for fruit and vegetable intake.⁶ But is this really a problem?

Some low-carb diet experts would say no, and that it is possible to meet the needs for essential nutrients with fewer servings of fruits and vegetables.

If someone feels better or improves certain health markers by avoiding all fruits and vegetables, one might ask if it’s healthy to do this long-term. We don’t know the answer to that question, and therefore we suggest experimenting with different types of fruit and veggies to see if some are tolerable.

Although blog posts, online support groups, and growing clinical experience report improved short-term health for many people following this style of eating, there are currently no data to support this as equally healthy or better than a diet that includes plants.⁷

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Health organizations state that their recommendations for fruit and vegetable intake are evidence-based. But as we’ve discussed previously in other guides, there are different levels of scientific evidence. And almost all these fruit and vegetable recommendations are designed for someone who is eating a standard Western diet or a low-fat, high-carb diet.⁸

Let’s explore the high-quality evidence available to see whether eating more fruits and vegetables has actually been proven to improve health.

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4. Research on the benefits of eating fruits and vegetables

Obesity

With few exceptions, eating more fruits and vegetables is standard weight-loss advice. But if we look at the results of experimental trials in which people ate more — or at least were encouraged to eat more — of these foods, we find that the majority of studies show little to no benefit for weight loss.

A 2014 systematic review of eight randomized controlled trials (RCTs) lasting between 4 and 52 weeks found that people assigned to increase their fruit and vegetable intake lost an average of only 1.5 pounds more than those assigned to eat smaller amounts of these foods.⁹

The same year, researchers who published a systematic review of seven different RCTs failed to find any measurable differences in weight change between people who consumed high vs. low amounts of fresh produce.¹⁰

In other studies, people who ate more fruits and vegetables actually gained weight, presumably because they didn’t compensate by cutting back on other foods.¹¹

On the other hand, if we focus on replacing highly-processed food with fruits and vegetables, it might lead to weight loss.

In a three-month study, overweight women who were given vouchers to purchase fresh produce lost 6 pounds, whereas those who were given vouchers to purchase any type of groceries gained 4 pounds by the study’s end.¹²

As we have said before, the overall diet likely matters more than individual foods.

Given that the results of most clinical trials have been disappointing when it comes to demonstrating weight loss with increased fruit and vegetable intake, what is the basis for the ubiquitous advice that this is key to achieving and maintaining a healthy weight?

For decades, it’s mainly been larger yet lower-quality observational (also called epidemiological) research.

For instance, a 2015 systematic review analyzing 17 such studies found statistically weak associations between eating a lot of produce and lower body weight and waist size.¹³

What were the odds ratios (ORs) in this study? They were 0.83 for high intake of fruits or vegetables alone and 0.91 for high intake of fruits and vegetables combined. While these modest odds ratios could reflect a tendency of fruits and vegetables to be associated with mild weight loss, they could also be a result of healthy user bias or other confounders commonly found in epidemiological data. Even the study authors acknowledged that “The present meta-analysis seems to be limited by low study quality.”

Guide to observational vs. experimental studies

Guide In this guide, we discuss the differences between observational and experimental studies, the advantages and disadvantages of each, and why in nearly all cases observational research shouldn’t be used when making decisions about your diet.

Diabetes and metabolic syndrome

Fruits and vegetables are generally considered diabetes-friendly foods. In fact, many types of produce make the “low GI foods” list on the American Diabetes Association website. Notable exceptions include melons, pineapple, and dried fruits such as dates, raisins, and cranberries.

But how does adhering to “5 a day” or similar dietary advice affect blood sugar control and insulin resistance? The evidence from clinical trials is mixed.

One systematic review of eight RCTs examining the effects of fruit and vegetable intake in people with metabolic syndrome found that, although diastolic blood pressure slightly improved in those who ate more produce, fasting blood sugar levels were no different among the groups.¹⁴

In one RCT published in Diabetes Care — a journal of the American Diabetes Association — researchers assigned overweight adults to consume two, four, or seven portions of fruits and vegetables per day for 12 weeks. Ultimately, none of the groups experienced any improvement in insulin resistance.¹⁵

However, results from another RCT found that a powder derived from broccoli sprouts lowered insulin levels and improved insulin sensitivity in adults with type 2 diabetes.¹⁶

Of course, none of the above studies specifically looked at people consuming low-carb or keto diets. It’s unknown whether adding broccoli or other green vegetables to a low-carb or keto diet would further reduce insulin resistance.¹⁷

What about lower-quality observational studies that suggest eating plenty of fruits and vegetables can help protect against type 2 diabetes? Large meta-analyses of these studies have shown very weak associations between fruit and vegetable intake and type 2 diabetes risk.¹⁸

Heart disease

Are fruits and vegetables heart-healthy? Although some experimental research suggests that eating more produce might reduce some cardiovascular disease (CVD) risk factors, the evidence to date is inconclusive with respect to clinical outcomes.

For instance, in 2013 researchers conducted a systematic review of 10 RCTs investigating whether eating more fruits and vegetables led to improvements in heart health markers. Although individual trials didn’t show impressive results, pooling the data suggested at least some favorable effect on cardiovascular risk factors (e.g. blood pressure and cholesterol).¹⁹

Another systematic review of both intervention trials and prospective cohort studies found that high potassium intake seemed to be beneficial for the arteries, while the effects of high fruit and vegetable intake on arterial function weren’t clear.²⁰

Some RCTs suggest that boosting produce intake may increase blood levels of antioxidants that could improve HDL function and reduce inflammation in those at high risk for CVD, such as those with diabetes.²¹

Yet others found no reduction in CVD risk factors in overweight people who consumed seven servings of produce per day compared to those who consumed two servings per day for 12 weeks.²²

There is some suggestion of benefit in observational studies; but as usual, it is necessary to point out that this sort of nutritional epidemiology research is inherently very weak and can’t prove cause and effect.²³

It’s also important to recognize that it’s very difficult to assess the effect of a single variable dietary change on the risk of something like cardiovascular disease, which can take years to develop and manifest. This is why most organizations promote a general pattern of healthy eating.²⁴

Cancer

“Eating lots of fruits and vegetables can help reduce your cancer risk.” This message is taken verbatim from the website of the American Cancer Society. But is there strong scientific evidence that eating large amounts of fruits and vegetables will help protect you from cancer?

Although fruits and vegetables are whole foods that contain beneficial nutrients, it’s too early to make that claim for them. In fact, it’s too early to make that claim for any foods with certainty, because very little high-quality experimental research has examined how specific foods affect cancer risk and progression.

It’s known that damage to DNA in cells may raise the risk of developing cancer in the future. One randomized cross-over study in healthy people found that consuming kiwifruit for three weeks led to increased antioxidant activity that helped repair DNA, regardless of whether small or large amounts were consumed.²⁵

Similar results were seen in young male smokers who consumed three servings of broccoli per day for 10 days.²⁶

However, other studies haven’t shown any improvement in DNA repair in people who increased their fruit and vegetable intake.²⁷ And one even suggested that cruciferous vegetables may temporarily damage DNA, although this effect seems to disappear within several hours.²⁸

Can healthy people reduce their chance of developing cancer by consuming antioxidants found in plants? At this point, we don’t know. After all, our bodies have their own built-in antioxidant systems in place that  can help repair cell damage.²⁹ Additional trials exploring the effects of fruits and vegetables on DNA repair would give us more information about this.

Cruciferous vegetables like broccoli and cabbage contain compounds that might help reduce cancer risk in several ways, such as decreasing inflammation and improving cell signaling.³⁰

Yet it appears there’s probably a threshold above which more of these protective compounds cannot be absorbed, so that very high intakes offer no further benefit than consuming more modest amounts.³¹

Many fruits and vegetables have other phytochemicals (literally “plant chemicals”) with potential anti-cancer activity, such as resveratrol and sulforaphane.³² However, their effects have been studied mainly in test tubes and animals. High-quality human research is needed before any conclusions can be made about their utility in cancer prevention or treatment.

In contrast to the limited amount of experimental research, plenty of observational studies have explored the relationship between fruit and vegetable intake and cancer risk. Researchers who conduct systematic reviews of these studies often conclude that people who eat the most fruits and vegetables decrease their risk of developing cancer.

As usual, these analyses cannot infer causality, but they reveal weak associations (RRs of 0.78 to 0.92) between eating a lot of produce and being diagnosed with any type of cancer, including breast, lung, colon, bladder, and non-Hodgkin’s lymphoma.³³

In summary, eating fruits and vegetables — especially cruciferous types — may very well decrease your risk of cancer, but much more rigorous research is needed before we can say this definitively.

Diet and cancer: What we know and what we don’t

Guide In this guide, we’ll look at what we know — and what we don’t know — about food and cancer.

Other conditions

Nearly all research on the benefits of fruit and vegetables for other conditions is observational, but a couple of experimental studies suggest potential benefits:

• Bone health: Results from one RCT found that increasing intake of certain fruits, vegetables, and herbs may improve bone health. Postmenopausal women who ate the “Scarborough Fair” diet — which included daily servings of leafy greens, cabbage, onions, mushrooms, prunes and, of course, parsley, sage, rosemary, and thyme (remember the old Simon and Garfunkel song?) — experienced less bone breakdown and calcium loss than women who consumed their usual diets or added other types of plants to their diets.³⁴
  In addition, a meta-analysis of both observational studies and RCTs found an association between an increased intake of fruits and vegetables and a decrease in the risk of fractures.³⁵
• Psychological health: A two-week study investigated the potential mental-health benefits of increasing fruit and vegetable intake in young adults who typically consume very little of these foods. The study participants reported improvements in well-being and motivation but no changes in depressive symptoms or overall mood.³⁶

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5. Can eating fruits and vegetables cause health problems in some people?

Most of us can eat a moderate portion of vegetables without any problems. Because they’re higher in sugar, fruits are generally best enjoyed in smaller quantities. However, for some people, both fruits and vegetables may cause issues.

Although there isn’t much published research about sensitivities to specific compounds found in fruits and vegetables, it is possible a small minority of people may have an unpleasant reaction to fruits and vegetables. This might be related to:

• Salicylates: Salicylates are found naturally in some fruits and vegetables.³⁷ Fruits and vegetables high in salicylates include berries, oranges, pineapples, apricots, broccoli, cucumbers, and zucchini.
• Oxalate: People who suffer from oxalate-containing kidney stones may have an increased frequency of stone formation if they over-consume fruits and vegetables high in oxalate.³⁸ Spinach contains much more oxalate than any other vegetable, but rhubarb, beet greens, kale, and other leafy greens also contain large amounts.
• Histamines: Your body releases histamine on its own as part of an immune response, but in rare conditions people can have excessive levels or an inability to break it down, and histamine can cause symptoms like hives, abdominal pain, asthma, and headaches.³⁹ High-histamine foods include eggplant, spinach, tomatoes, sauerkraut, and avocados.
• FODMAPS: This is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These sugar molecules — found most often in fruits, vegetables and grains — can cause digestive upset in people with irritable bowel syndrome (IBS). People with IBS often find reducing or eliminating FODMAP foods greatly improves their symptoms.⁴⁰

If you suspect you may have one of these sensitivities, keep in mind that processed, canned, and fermented foods also contain some of these compounds. Your symptoms might also be due to another health issue. Be sure to see a doctor for a full work-up to rule out other causes.

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6. Will avoiding fruits and vegetables lead to nutrient deficiencies?

Many people feel that fruits and vegetables are indispensable for health because they provide important vitamins and minerals. While it’s true that they contain several micronutrients and phytonutrients which could play important roles in the maintenance of good health, it’s important to recognize other minimally processed foods can help meet your needs.

Meat, fish, eggs, and dairy provide many essential vitamins and minerals. For example, dairy is a great source of potassium and magnesium. Organ meats like chicken liver and beef kidney are good sources of vitamin C.⁴¹ Hence, eating a varied, low-carb diet – with a mix of low-carb fruits and vegetables – will help you meet your nutrient needs for vitamin C, potassium, folate, and other key nutrients.

What about fiber? Although fiber isn’t an essential nutrient, many health organizations recommend a daily minimum of 25 grams per day for adults.

Some believe that low-carb diets are inherently low in fiber. But that simply is not true. Nuts and seeds, avocado, berries, coconut, and many non-starchy veggies are all high-fiber foods you can enjoy on a low-carb diet.

You can read more about the science behind fiber intake in our guide on whole grains.

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7. Summary – fruits and vegetables: optional, optimal, or essential?

Fruits and vegetables are whole foods that provide vitamins, minerals, and fiber, along with other potentially beneficial compounds like phytonutrients.

In addition, many people — although certainly not all — genuinely enjoy the taste and texture of low-carb fruit and veggies, especially when combined with a fat or tasty sauce. Think creamed spinach, zucchini noodles fettuccine with olive oil and butter, or berries with cream.

Moreover, there’s no question that replacing high-carb processed foods with fresh fruits and vegetables is a healthy move. And above-ground vegetables can play an important role in higher satiety eating.

It is possible – though not definitively proven – that fruits and vegetables play an independent role in reducing disease risk. In the case of cruciferous and leafy green vegetables, it seems likely.

As always, we advise considering fruits and vegetables in the context of your whole diet. If you find that following a low-carb diet helps you lose body fat and get your diabetes or prediabetes under control, this is what will have the greatest impact on your overall health. With this strategy, you can still eat a variety of low-carb vegetables and some fruits to obtain the potential benefits.

/ Franziska Spritzler, RD

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