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Western nutritionists recommend that a substantial part of a healthy diet include fruit, vegetables and grains.

e.g.

  • Nutrition Australia's Healthy Eating Pyramid (via Vuly):

    Healthy eating pyramid Click to enlarge.

  • Harvard University's Healthy Eating Plate

    Healthy Eating Plate Click to enlarge.

However, in the Mongolian cuisine, fruit, vegetables and grains are rare, and Mongolians have a life expectancy from birth of 69.8 years, compared to the people of Laos, who eat a lot of fruit, vegetables and grains, but who only have a life expectancy of 65.8 years.

Is the advice to eat a lot of fruit, vegetables and grains sound?

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    Only in an affluent society can you choose your diet. Everyone else eats what is available. The tide of opinion from experts about what is healthy swings to and fro, for example is butter good or bad? – Weather Vane Feb 12 at 16:03
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    You picked two more or less random countries to compare and with a live expectancy of 70 Mongolia is at the lower end internationally as well. Why did you compare to Laos as opposed to any other country? – quarague Feb 13 at 7:44
  • @quarague If it was unhealthy to eat meat and drink milk mainly, a Mongolian should die earlier at the age of 40 or 50 since local medical facilities are bad. A Westerner may also be seriously ill at 60 and would die if there were not a good hospital. Then life expectancy wouldn't be so high in the West. So whether one eats a lot of vegetables, grains and fruit may not be the decisive factor that influences health. The Laotians are the negative example. – Allan Feb 13 at 13:02
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Summary

  • There is some evidence that high consumption of plant foods can be associated with better health but not necessary with increased life expectancy, as observed in studies in vegetarians (Crit Rev Food Sci Nutr.).
  • Comparison of plant food intake and life expectancy by country makes no sense without considering other factors, such as genetics, medical care availability, etc. India has the highest percent of vegetarians (31%) and one of the lowest meat intakes (4.4 kg/person/year), but their life expectancy is only 69.4 years.

Is the advice to eat a lot of fruit, vegetables and grains sound?

In general, plant foods can be helpful, because:

1) Plant foods contain dietary fiber, which contributes to bowel regularity.

Effect of dietary fiber on constipation: A meta analysis (World Journal of Gastroenterology, 2012):

In summary, our meta-analysis demonstrated that dietary fiber can obviously increase stool frequency in patients with constipation.

2) Plant foods are, in general, less energy dense than animal foods, so they can be more satiating and thus help to maintain healthy body weight.

A plant-based diet for overweight and obesity prevention and treatment (Journal of Geriatric Cardiology, 2017):

In summary, individuals consuming PBDs tend to have lower BMI than those consuming non-PBDs. The adoption of PBDs also appears effective for weight loss. (PBDs = plant-based diets ; BMI = body mass index = kg/height in m2)

3) Vegetarian/vegan diets have been associated with lower risk of heart disease and cancer.

Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies (Critical Reviews in Food Science and Nutrition, 2017):

With regard to prospective cohort studies, the analysis showed a significant reduced risk of incidence and/or mortality from ischemic heart disease (RR 0.75; 95% CI, 0.68 to 0.82) and incidence of total cancer (RR 0.92; 95% CI 0.87 to 0.98) but not of total cardiovascular and cerebrovascular diseases, all-cause mortality and mortality from cancer.

4) Plant foods can be beneficial for health, but it's not clear why.

The effects of plant-based diets on the body and the brain: a systematic review (Translational Psychiatry, 2019):

Based on this systematic review of randomized clinical trials, there is an overall robust support for beneficial effects of a plant-based diet on metabolic measures in health and disease. However, the evidence for cognitive and mental effects of a plant-based diet is still inconclusive. Also, it is not clear whether putative effects are due to the diet per se, certain nutrients of the diet (or the avoidance of certain animal-based nutrients) or other factors associated with vegetarian/vegan diets.

BUT, there is no reliable evidence to advise how much plant foods one needs to consume to have health benefits from them. The 2015–2020 Dietary Guidelines for Americans recommends that people needing 2,000 calories per day include 2 cups of fruit and 2.5 cups of vegetables per day (USDA.gov), but this amount is not clearly based on any evidence.

Are there any harms side effects of high plant food intake?

This depends on the person and his/her underlying health disorders.

  • In general, high intake of plant foods high in soluble fiber (barley, oats, rye, legumes, apples, prunes, pears, bananas) can result in excessive abdominal bloating and flatulence.
  • In individuals with fructose malabsortion, plant foods high in fructose (apples, pears, onions, agave...) can result in bloating and diarrhea.
  • In individuals with hereditary fructose intolerance, even minute amounts of fructose or sucrose (in fruits, nuts and many vegetables) can cause severe kidney and liver problems or even death.
  • In individuals with oxalate kidney stones, avoidance of foods high in oxalates (spinach, rhubarb, nuts, legumes...) can decrease the risk of new stones.

Plant food intake and life expectancy by country

Comparison of plant food intake (concluding from meat intake, which is roughly inverse to plant food intake) and life expectancy by country is not helpful because other factors, such as genetic and environmental factors, availability of medical care, economical status, etc. can override the effect of high plant food intake on life expectancy in a negative or positive way. For example:

  • Bangladesh: meat: 4 kg...exp: 72.3 y.
  • India: meat: 4.4 kg...exp: 69.4 y.
  • Japan: meat: 45.9 kg...exp: 84.5 y.
  • China: meat: 58.2 kg...exp: 76.7 y.
  • Brazil: meat: 85.3 kg...exp: 71.4 y.
  • Germany: meat: 88.1 kg...exp: 81.2 y.
  • United States: meat: 120.2 kg...exp: 78.9 y.
  • (meat = kg of meat available to a person/year, exp = life expectancy)
| improve this answer | |
  • The 'by country' section seems to be in direct contradiction to the strong opening with "there is evidence"? Since I'd say that is only 'suggestive' or 'used to justify'. All I ever see is parameterised input values and correlations, but never a convincing bottom line. Even the "worst diet in the world" (Scots) has as many confounding factors attached to the whole situation as Jeanne Calment is the poster girl for futility re-applying statistically inferred knowledge back to sound individual advice. Depends. We know especially this: we have limited insight as our poor predictions prove. – LangLаngС Feb 13 at 16:37
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    OK, I emphasized what I believed it was clear: The country section data by themselves have no sense, so they don't prove or disprove anything and I see no conflict. – Jan Feb 13 at 16:53
  • It's a considerably diminished risk with modern agricultural practices, human food preparation rituals, and our general thumbing of noses at natural poisons, but there is a minor risk of accumulations of poisons with most plants having some level of it to discourage over-grazing. Maybe not even worth mentioning, though, as you'd have to have someone pursuing an unhealthy raw foods diet with over-consumption, or someone with an innate intolerance to the natural poisons. – Sean Duggan Feb 14 at 18:28
  • @SeanDuggan, this also applies to animal foods, doesn't it? – Jan Feb 14 at 18:30
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    @Jan: To some degree. Polar Bear livers are a bad thing to eat unless you want to have your skin peel off. Fugu is marketed for being deadly if not prepared correctly. Lobsters taste lousy unless you boil them alive. But, because plants have fewer active defenses, they're more prone to having those poisons. Which, as I noted, humans are so resistant to that we use poisonous plants to spice up our food. There's a reason why nutmeg is deadly for dogs. – Sean Duggan Feb 14 at 18:39

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