From study:
"Sufficient intake of fruits and vegetables has been associated with a reduced risk of chronic diseases and body weight management but the exact mechanism is unknown."
Association does not equal cause and effect. They can't pinpoint mechanism.
"Various reviews have associated low intake of fruits and vegetables with chronic diseases such as cardiovascular diseases, blood pressure, hypercholesterolemia, osteoporosis, many cancers, chronic obstructive pulmonary diseases, respiratory problems as well as mental health (2–6)."
Association does not imply causation, there are confounding variables. The study I provided was a randomized controlled trial where things were more controlled.
"Sufficient intake of fruit and vegetables (F&V) has been related epidemiologically with reduced risk of many non-communicable diseases."
Related epidemiologically does not imply causation. Cause and effect still remains to be proven.
"Several studies have highlighted the CVD risk-reducing potential of F&V whereby their intake were strongly associated with lower cardiovascular risk factors such as lower blood pressure (BP), cholesterol and triacylglycerol thus preventing premature cardiovascular disorders (2)."
Association again. No cause and effect.
"Moreover, fibers found in F&V have been shown to reduce intestinal passage rates by forming a bulk, leading to a more gradual nutrient absorption (10) hence preventing constipation. They can be fermented in the colon, increasing the concentration of short chain fatty acids having anticarcinogenic properties (11) and maintaining gut health."
When looking at supporting evidence for this, here is what I find:
"Epidemiological and clinical studies demonstrate that intake of dietary fiber and whole grain is inversely related to obesity, type two diabetes, cancer and cardiovascular disease (CVD)."
Again, no cause and effect.
"Generally speaking, dietary fiber is the edible parts of plants, or similar carbohydrates, that are resistant to digestion and absorption in the small intestine. Dietary fiber can be separated into many different fractions. Recent research has begun to isolate these components and determine if increasing their levels in a diet is beneficial to human health. These fractions include arabinoxylan, inulin, pectin, bran, cellulose, β-glucan and resistant starch. The study of these components may give us a better understanding of how and why dietary fiber may decrease the risk for certain diseases.
The mechanisms behind the reported effects of dietary fiber on metabolic health are not well established. It is speculated to be a result of changes in intestinal viscosity, nutrient absorption, rate of passage, production of short chain fatty acids and production of gut hormones.
Given the inconsistencies reported between studies this review will examine the most up to date data concerning dietary fiber and its effects on metabolic health."
"Recently Habauzit et al. (12) reported that fruits containing a high amount of anthocyanins, flavonols and procyanidins, such as berries, grapes and pomegranate are effective at decreasing cardiovascular risk while citrus fruits and apples had a moderate effect on BP and blood lipid level. "
I don't know how they came to this conclusion, whether the evidence for it is solid. Don't have access to full study.
"An increased consumption of carotenoid-rich F&V maintains the cholesterol level in blood since they reduce oxidative damage and cause an increase in LDL oxidation resistance (13)."
Cholesterol level has been shown not to be a consistent predictive factor for heart disease and some with heart disease, atherosclerosis have low levels while others have high levels. The findings are mixed and there is no strong evidence for its causal relationship.
"An increased consumption of cruciferous vegetables was also reported to cause a decrease in the risk of intestinal, bowel, thyroid, pancreatic and lung cancer (4)."
Let's see what this is based on
"There have been several reports in recent years which have reviewed the epidemiological evidence that increased consumption of fruit and vegetables reduces the risk of cancer[2]. Of 156 publications reviewed, 128 showed a statistically significant positive correlation between increased fruit and vegetable consumption and a decreased risk of cancer. Further evidence was presented in a comprehensive review[3]."
Correlation does not equal cause and effect.
"In this review, increased consumption of cruciferous vegetables (broccoli, Brussels sprouts, cabbage, cauliflower, etc.) was correlated to a reduction in the risk of intestinal, bowel and thyroid cancer. Carrots, fruit and cruciferous vegetables were correlated with reduced incidence of pancreatic cancer, and carrots and leafy green vegetables were protective against lung cancer. The reductions in relative risks are summarized in Table I."
Same as above.
"F&V have also been
suggested to prevent osteoporosis in adults mainly for their rich sources of calcium and other vitamins which are vital in bone health (3). The high fiber content of F&V
may play a role in calcium absorption and reduce the 'acid load' of the diet (14) enhancing bone formation and suppressing bone resorption which consequently result in greater bone strength (15)."
Speculation, nothing more.
"Moreover, phytoingredients in F&V such as gooseberry, curcumin, and soya isoflavones have shown to be protective against lens damage which occurs due to hyperglycemia (16) and certain flavonoids such as quercetin can prevent oxidative stress in the pathogenesis of glaucoma (17)."
Based on the following research:
"The present scenario indicates that the majority of research uses
experimental animals and in vitro experiments. Foods or phytoingredients such as gooseberry, curcumin, and soya isoflavones have shown promising potential in the control of lens damage occurring because of hyperglycemia."
Not convincing at all. Should be tested in humans, in vivo.
About the flavonoids, again, this is based on in-vitro studies and not tested in humans.
"Also, a high intake of F&V was inversely associated with the risk of COPD and respiratory symptoms (5). Higher total fruit and vegetable intake is also associated with lower risk of cognitive decline hence proved beneficial for mental health (6, 18). "
Always associations, nothing more.
"Based on available evidence, a clear relationship between F&V and diseases has been well established"
Relationship but no causal relationship which is really what we need to determine to get at solid and conclusive facts.
"Green leafy vegetables, rather than fruit, were
suggested to have a genuine protective effect against lung cancer (19)."
Speculation.
"further studies are warranted."
Indeed! I agree.
And it's the same old stuff, repeated again and again, in the next section. In-vitro studies looking at factors in isolation and associations/correlations.
Here is an interesting statement:
"Hence an increased FVI can help to ease weight loss and this can be achieved when F&V displace high-energy-dense foods such as saturated fats, sugar (30) so that the overall energy density of the diet is reduced (31). "
Grouping together saturated fats and sugar when clearly their effects on the human body differ significantly. Plenty of studies have shown that in the presence of higher saturated fat and lower overall carbs, people lose weight and health improves significantly. This has been shown time and time again, since the late 1800's. One need just think of the Masai, the Inuits, the French and the Swiss who despite eating more saturated fat than their American counterparts, are, on average, thinner and in better health.
Another one:
"Fibers also form a gel-like environment in the small intestine, resulting in reduced activity of the enzymes involved in the digestion of fat, protein and carbohydrates (29)."
And that's a good thing?? Reducing macronutrient and nutrient absorption??
"It is also understood that fruits and non-starchy vegetables are very low in energy since they contain high amount of water and fiber and can be consumed in a relatively larger amount contributing to increased satiety to maintain normal weight (28)."
Consumed in higher amounts, the energy consumed goes up so you end up ingesting as much calories. You just need to consume much much more relative to other foods but the end result is the same. Too much fructose in fruits can also lead to buildup of fat in liver, beware! Today's fruits are sweeter than before and poorer in nutrients. Genetically modified.
"High consumption of fructose in F&V is related to obesity in rodents but no effect has yet been demonstrated in humans (34). FVI in over-weight and obese people is much lower than the recommendation since they tend to restrict intake of these F&V when trying to lose weight."
The rest is about phytochemicals and other substances found in fruits and vegetables tested in isolation. Not quite applicable to real life effects where the concentrations might differ and overall results might prove to be quite different.
All the rest are associations.
So, overall, not very convincing at all. We need stronger evidence, controlled trials, one of which was provided to you above.
It's important to take the time to really read the full study, check the references, look at details before jumping to conclusions as you might be surprised at how weak the evidence is for establishing those recommendations.
Show me cause and effect in human beings and at least we have something more solid to work with.
