As a vegetarian of more than 15 years, I endeavour to have a diet that is varied and contains protein and iron-rich foods. Having a conversation the other day with someone about the number of eggs that I consume a day (2 -3 per day), my conversational partner asked if I was worried about the effect of the eggs on my cholesterol levels. Having had my cholesterol tested, I am not so worried, but the remark made me think of some the regularly cited food myths. These include eggs cause high cholesterol, mushrooms are ‘meat’ for vegetarians and spinach is high in iron. So I thought in this weeks post, I would debunk or confirm these food myths.
Myth: Eggs cause high cholesterol
Cholesterol is an important natural molecule that can be obtained from the diet, or produced by our cells. It can be used to make cell membranes as well as act as a precursor for steroid hormones. When cholesterol intake from the diet is high, the body produces less of its endogenous cholesterol and vice versa. Cholesterol is carried around the blood to muscles and tissues in carrier molecules containing lipopolysaccharides that are defined by their density in the plasma – high density lipopolysaccharides (HDL) and low or very low density lipopolysaccharides (LDL/VLDL). HDL particles can remove cholesterol from cells back to the liver, meaning that serum cholesterol levels are lower, while LDL/VLDL transport and deposit cholesterol to cells in vascular walls, leaving the cells to form ‘plaques’ that restrict blood flow and can lead to heart attacks, strokes and cardiovascular disease.
As it was known that cholesterol can be obtained from the diet, dieticians and clinicians advised individuals who fell into a high risk category for heart disease to reduce their consumption of foods high in fat and cholesterol. Amongst these were eggs. This advice to remove eggs from the diet came from early animal experiments that suggested eggs raise serum cholesterol levels. However, further studies, including large randomised human studies, have since shown that while eggs do contribute to serum cholesterol levels, there is no substantial evidence to indicate that they increase the risk of heart disease. In fact, one study showed that eggs increased beneficial liver enzymes and HDL levels, thus lowering the VLDL/LDL cholesterol levels.
Myth: Mushrooms are ‘meat’ for vegetarians
One of the challenges for a vegetarian is to maintain adequate protein consumption. Dietary proteins are crucial to cells as they are broken down to their composite molecules that are then used to produce other molecules required by the cell. Animal meat is without a doubt the easiest way to obtain dietary protein. Thus for someone who chooses not to eat meat, finding a high plant-based protein source is a challenge.
Most Australians will remember an advertising campaign from the 1990s whose tag line was “mushrooms…..they’re meat for vegetarians’’, and thus a generation of vegetarians added mushrooms to their diet as a protein source. But, is this actually true? It appears that the general consensus is that early measurements of mushroom protein levels were vastly over estimated and possibly influenced by the soil they were grown in, and that protein levels are not high enough to be a complete meat protein substitute. But let’s not completely write off mushrooms for their nutritional value, as it appears that they are a rich source of vitamin B12.
Myth: Spinach is a good source of iron
We have all grown up with the imagery and advertising that spinach is a good source of iron, I mean, Popeye ate spinach to make him strong! It’s true, that when we look at the level of iron and how much it can contribute to the daily-recommended intake, spinach is a rich source. The bad news is that spinach also contains high levels of a group of molecules called oxalates, which can inhibit the absorption of iron. There are also other food-based compounds that can inhibit iron absorption such as the tannins found in tea and coffee. However, chemicals such as ascorbic acid (Vitamin C) enhance iron absorption. Therefore, it is recommended to eat your leafy greens or take your iron tablets with a glass of orange juice. Interesting side note, alcohol is also an enhancer of dietary iron!
Myths busted or confirmed?
Of the food myths, both the eggs and mushroom myths were busted, and the spinach myth was confirmed. It seems that quite often a food myth is attenuated through popular culture, and in the case of the mushrooms, the Mushroom Growers’ advertising campaign.
A Final thought. All the articles I read on these myths came to the same conclusion, that no one food can be a substitute for a healthy, well-rounded and balanced diet.
Klucken, J et al. (2000). ABCG1 (ABC8), the human homolog of the Drosophila white gene, is a regulator of macrophage cholesterol and phospholipid transport. Proceedings of the National Academy of Sciences, 97(2), 817-822.
Missimer, Amanda, et al. “Intake of 2 eggs or oatmeal for breakfast does not increase biomarkers for heart disease while eggs improve liver enzymes and raise HDL cholesterol in young healthy individuals.” The FASEB Journal 29.1 Supplement (2015): 274-2.
Kalač, Pavel. “A review of chemical composition and nutritional value of wild‐growing and cultivated mushrooms.” Journal of the Science of Food and Agriculture 93.2 (2013): 209-218.
Wani, Bilal Ahmad, R. H. Bodha, and A. H. Wani. “Nutritional and medicinal importance of mushrooms.” Journal of Medicinal Plants Research 4.24 (2010): 2598-2604.
Noonan, S. C., and G. P. Savage. “Oxalate content of foods and its effect on humans.” Asia Pacific Journal of Clinical Nutrition 8 (1999): 64-74.
Abbaspour, Nazanin, Richard Hurrell, and Roya Kelishadi. “Review on iron and its importance for human health.” Journal of Research in Medical Sciences 19.2 (2014).
Collings, Rachel, et al. “The absorption of iron from whole diets: a systematic review.” The American journal of clinical nutrition (2013): ajcn-050609.