The Egg Conundrum
Eggs have a high nutrient density per calorie and contain an accessible and inexpensive, comprehensive inventory of virtually every nutrient needed for brain health. Simply adding whole eggs to the diet of stressed rats reduces their depression. In a small study, giving depressed humans egg powder, relieved their symptoms. Eggs can be a magnificent weapon in an anti-stress armoury.
Although it is becoming apparent that eating eggs may not result in as great a seismic shift in blood cholesterol levels as previously feared, our knowledge regarding eggs and metabolic/cardiovascular disease is still studded with some gaping holes. In the past, if one's cholesterol levels teetered towards the higher half of normal, even a single egg would be a guilty pleasure enjoyed in the style of The Last Supper before the (assumed) onslaught of atherosclerosis. The pendulum has swung from one extreme to another. Where the egg-phobe of the past would refuse to entertain the possibility that eggs might do good, the egg-phile of the present defiantly brushes away the notion that eggs could, in specific settings, cause harm. Australians crack 19 million eggs a day and there is currently a ‘scramble’ for eggs in Australia after a 3.5% rise in egg intake over the past year.
Long-term nutrition studies are notoriously difficult to conduct and are mired with poor participant memory, unpredictable changes in behaviour/eating patterns and loose observation. Nonetheless, they are often all we have to go by. When it comes to eggs, they paint an interesting picture. In the setting of a low carbohydrate diet, where carbohydrates are restricted to 10-15% of the overall caloric intake (and hence the diet contains no refined carbohydrates), eating three whole eggs every day (that’s 640 mg/d of dietary cholesterol) has been shown to raise HDL cholesterol (the kind commonly referred to as ‘good’, without raising LDL cholesterol (the kind commonly referred to as ‘bad’) in overweight men aged 40-70 years, suggesting that, contrary to popular belief, eggs have a beneficial effect on cholesterol levels. On the other hand, when over 23,000 seemingly healthy Korean men and women went through a health screening procedure, those who ate seven or more eggs a week had more atherosclerosis than those who had six fewer eggs a week. The atherosclerosis correlated with cholesterol levels and was worse in those who did not have a high vegetable intake and in those with a higher BMI. In this setting, eggs seemed to have a harmful effect. When two cohorts from two separate Swedish studies ( 37,766 men and 32,805 women) were followed up for 13 years, eating seven or more eggs a week raised the risk of heart failure just like in the Korean study. The pendulum swings back yet again: another cross sectional study did not find an association between coronary artery disease and egg intake, even in the presence of the ApoE4 allele, which can increase coronary artery disease risk. A study from northern Manhattan found that eating eggs was inversely associated with carotid artery atherosclerosis. In Australia, a randomized study on overweight or obese individuals with pre-diabetes or type II diabetes, showed eating twelve eggs a week did not affect cholesterol levels after three months compared to eating less than two eggs, in the context of a calorie-restricted diet containing monounsaturated and polyunsaturated fats, similar in style to a Mediterranean diet.
The effect of a particular food is the result of what else is being eaten with it. Refined food restriction/caloric restriction/a Mediterranean style diet and three eggs a day seems to have a different effect to eating three eggs a day as part of a careless, ad-libitum diet that is low in vegetables, is based on processed food, and is excessively high in calories.
While there appears to be an association between type II diabetes and egg intake in the United States, in a Spanish, prospective, cohort study following almost 16,000 participants over a median of 6.6 years, no association was found between eating eggs and succumbing to type II diabetes, perhaps on account of their Mediterranean diet. There is also no association between type II diabetes and egg intake in Sweden, where the baseline diet is different.
The effect of eating eggs on cardiovascular disease and diabetes appears to depend on the baseline diet. If the baseline diet promotes cardiovascular disease or diabetes, eggs might make things worse; otherwise, eggs may not cause harm and may even improve cholesterol profile. A diet that is high in antioxidants may have a protective effect on atherosclerosis. The oleic acid in monounsaturated fats might protect against the palmitate in eggs (the long chain saturated fat palmitate has been associated with inflammation and insulin resistance). Eggs are a rich source of dietary choline. Gut bacteria can convert the choline in our diet to a product known as TMAO, which has been linked to atherosclerosis (though this link has proven difficult to explain in some instances). Some types of extra virgin olive oil and balsamic vinegar contain a compound called DMB which may prevent gut bacteria from converting choline into TMAO, hence reducing atherosclerosis. Gut bacteria may themselves play a key role here and a plant-based diet may nurture a more beneficial gut bacterial profile. This may contribute to the benefits of a Mediterranean diet. It may also be that people who are not careful about their diet overall may eat eggs with abandon, which associates egg consumption with atherosclerosis and diabetes, even if the eggs are not causing the disease. We still don’t have all the answers and must wait for more empirical evidence.
If you are fond of eggs and want to tap into their ‘brain health’ goodness, you could take advantage of all the studies so far and cushion your egg intake within a dietary ‘safety’ scaffold. This is the strategy I use:
- Avoid refined foods of all kind.
- Do not overeat overall – stay within your calorie limits every day
- Follow a largely plant-based diet that promotes a healthy microbiota
- Try to base most of your fat intake on unprocessed, monounsaturated sources such as extra virgin olive oil
Until we know more, nutrition continues to remain an art rather than a science, where the the overall picture is different to the mere sum of its parts. Eating in this way is likely to change your canvas for the better and help buffer any harm.
Please note this information is for discussion only and should not be used as medical advice. Please consult your medical doctor before making any changes to your diet, lifestyle or medications.
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