BIOAVAILABILITY

“Even though some plants, such as spinach, are high in iron, the body can only absorb 1.4-7% of the iron in plants whereas it can absorb 20% of the iron in red meat.” https://www.ncbi.nlm.nih.gov/pubmed/1745900

“Deficiencies of iron, zinc, iodine and vitamin A are widespread in the developing countries, poor bioavailability of these micronutrients from plant-based foods being the major reason for their wide prevalence. Diets predominantly vegetarian are composed of components that enhance as well as inhibit mineral bioavailability, the latter being predominant.” https://www.ncbi.nlm.nih.gov/pubmed/25748063

“The limited bioavailability of antioxidants present in food from fruit and vegetable matrices is determined by their low bioaccessibility in the small intestine due to the physical and chemical interactions of the antioxidants with the indigestible polysaccharides of cell walls.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3052441/

Fiber affecting absorption of beta-carotene: https://www.ncbi.nlm.nih.gov/pubmed/1309477

“Healthy and diabetic women consume phytic acid in amounts that are likely to decrease the bioavailability of dietary zinc.” https://www.ncbi.nlm.nih.gov/pubmed/22528778

Bioavailability of vitamin B-6 from plant foods. https://www.ncbi.nlm.nih.gov/pubmed/2843032

“Poor digestibility of protein in the diets of developing countries, which are based on less refined cereals and grain legumes as major sources of protein, is due to the presence of less digestible protein fractions, high levels of insoluble fibre, and/or high concentrations of antinutritional factors present endogenously or formed during processing.” https://www.ncbi.nlm.nih.gov/pubmed/23107545

Low bioavailability/conversion of beta-carotene and provitamin A carotenoids to vitamin A in plants vs high bioavailability of vitamin A from animal foods. https://www.ncbi.nlm.nih.gov/pubmed/26115350

“Micronutrients of special concern for the vegan include vitamins B-12 and D, calcium, and long-chain n-3 (omega-3) fatty acids. Unless vegans regularly consume foods that are fortified with these nutrients, appropriate supplements should be consumed. In some cases, iron and zinc status of vegans may also be of concern because of the limited bioavailability of these minerals.” https://www.ncbi.nlm.nih.gov/pubmed/19279075

Vegans/Vegetarians at risk for choline deficiencies https://www.ncbi.nlm.nih.gov/pubmed/30853718

“The human brain cannot develop normally without a reliable supply of several nutrients, notably docosahexaenoic acid (DHA), iodine and iron.” https://www.ncbi.nlm.nih.gov/pubmed/16828044

PLANT ANTI-NUTRIENTS ​

“Green Smoothie Cleanse”: Causing Acute Oxalate Nephropathy” https://www.ncbi.nlm.nih.gov/pubmed/29203127

“Calcium was an important constituent in all the green leafy vegetables examined, but bioavailability was limited due to the presence of oxalate, tannin, phytate and dietary fibers.” https://www.ncbi.nlm.nih.gov/pubmed/25306367

“Therefore even when carotenoids are found in high quantities in plant foods their utilization may be unsatisfactory because some factors are known to interfere as negative effectors.” https://www.ncbi.nlm.nih.gov/pubmed/26168011

Having to bioengineer crops to have lower anti-nutrients so that they are safer to eat… https://www.ncbi.nlm.nih.gov/pubmed/25883599

“Although many edible plants are high in total Ca, complexation with oxalate (forming Ca-oxalate crystals) renders it undigestible.” https://www.ncbi.nlm.nih.gov/pubmed/23016135

Oxalic acid in spinach reduced calcium absorption in rats. https://www.ncbi.nlm.nih.gov/pubmed/3183773

“In conclusion, the results from the present study demonstrate that the mean fractional apparent Mg absorption from a test meal served with spinach was about 35 % lower than from a test meal served with kale [low in oxalates]. It is suggested that this reduction in Mg absorption is due to the higher oxalate content of spinach.” https://www.ncbi.nlm.nih.gov/pubmed/15035687

Lectins in plant foods as a possible underlying cause of Parkinson’s Disease. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4780318/

“Naturally occurring goitrogens: They are found in legumes, plants, amiodarone, lithium, in addition to cabbage, cauliflower, broccoli, turnip, forms of root cassava. Soy or soy enriched foods can also aggravate thyroid problems reducing T4 absorption and interfering with thyroid hormone action and are reported to increase auto-immune thyroid disease.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740614/

This study demonstrates a low bioavailability of iron from five commonly consumed legumes (soybeans, black beans, lentils, mung beans, and split peas). The authors suggest tannins and phytates, two plant compounds known to inhibit the absorption of iron, are contributing factors. https://www.ncbi.nlm.nih.gov/pubmed/6741854

INFERIORITY OF PLANT SOURCED VITAMINS

“Conversion of ALA by the body to the more active longer-chain metabolites is inefficient: < 5-10% for EPA and 2-5% for DHA.” https://www.ncbi.nlm.nih.gov/pubmed/12936959

“…no significant increase was detected in plasma eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) levels in any of the flax-fed groups [alpha-linolenic acid (ALA)]” https://www.ncbi.nlm.nih.gov/pubmed/18689552

“These data indicated that the bioconversion of β-carotene to vitamin A was not as efficient as expected, and, as a result, the Food and Nutrition Board recently revised the estimated efficiency factor for the conversion of dietary β-carotene to vitamin A from 6:1 by weight (20) to the new value of 12:1 by weight (21)… On the other hand, preformed vitamin A from animal origins or from supplements can be absorbed and stored in the human body very effectively.” https://academic.oup.com/ajcn/article/91/5/1468S/4597430

Poor bioavailability of plant sources of vitamin K (K1 - the form of vitamin K found in plants). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3321250/

“Menaquinones (K2), which are primarily derived from animal-based sources, are consumed in food matrices containing more fat that may improve absorption and lead to higher bioavailability than phylloquinone (K1)” https://www.ncbi.nlm.nih.gov/pubmed/23590754

“…it may be estimated from our data that less than 10 % of phylloquinone [K1] present in green vegetables is absorbed in the digestive tract. Although this is less than generally assumed, it leaves green vegetables as the main source of dietary phylloquinone. This conclusion implies that other sources of vitamin K may contribute significantly to human vitamin K status.” https://www.ncbi.nlm.nih.gov/pubmed/8813897

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LACK OF HEALTH BENEFITS OF PLANT FOODS ​

"No effect of 600 grams fruit and vegetables per day on oxidative DNA damage and repair in healthy nonsmokers."

https://www.ncbi.nlm.nih.gov/pubmed/14578137

“The overall effect of the 10-week period without dietary fruits and vegetables was a decrease in oxidative damage to DNA, blood proteins, and plasma lipids, concomitantly with marked changes in antioxidative defense.” https://www.ncbi.nlm.nih.gov/pubmed/12064344