Nutritional science is often drawing up new conclusions contradictory to what was previously thought. To outsiders, it may appear that scientists are changing their mind, sprouting new statements to suit whatever they want at the time. This is as far from the truth as you could get. Changing conclusions or recommendations in the light of new evidence is the beauty of science. It says that there is no pride lost in saying “we were wrong”, and “we’ll go wherever the data takes us”.
One of the latest swings in recommendations over the past few years has been the link between dietary cholesterol and blood cholesterol, with eggs being the highly scrutinised food at the forefront of this debate.
Why is Blood Cholesterol Important?
Cardiovascular Disease (CVD) is the leading cause of death not only in Australia, but in both developed and developing countries the World over. High levels of low density lipoprotein cholesterol (LDL-C), and low levels of high density lipoprotein cholesterol (HDL-C) in the blood are a risk factor for CVD. As is dyslipidaemia and high levels of blood triglycerides .
It makes sense then that any modifiable risk factors – such as diet, physical activity, and lifestyle – are at the forefront of public health policy, in the hope of reducing rates of CVD.
Dietary Cholesterol & Blood Cholesterol
Wind the clock back a decade or two and the evidence appeared to support the notion that there was a direct relationship between dietary cholesterol and blood cholesterol levels . It would come as no surprise then that dietary guidelines followed the evidence and suggested people steer clear of foods high in cholesterol.
Whilst advocates of plant based diets still argue that this is the case, the overwhelming amount of recent evidence is suggesting it is not in fact true . Organisations such as the Heart Foundation have now changed their recommendations, suggesting people not fear foods rich in cholesterol.
Eggs – From Unhealthy to Healthy
The best example of this is eggs; which are a rich source of nutrients but also cholesterol. Given the old dietary guidelines, eggs were once considered a bad food option for both individuals with high LDL levels and general population. With the recent scientific findings and amended guidelines, eggs are now considered a healthy food choice when consumed in moderation. Why moderation? They still contain high levels of saturated fat, which we will unpack soon.
How did they get things wrong?
Nutritional science is complex, and it appears that not enough scrutiny was paid to the differing effects of saturated fat and dietary cholesterol on the development of dyslipidaemia and atherosclerosis. We now know that most of the cholesterol in your body is manufactured by the liver. There are some population subgroups whose blood cholesterol may be impacted more by dietary cholesterol than others, however for most people any impact is fairly insignificant .
Saturated and Trans Fats
Whilst guidelines have been reversed concerning cholesterol, there has still been no movement in regards to saturated and trans fats, with evidence showing both to negatively impact blood cholesterol and disease risk [3, 4]. Saturated fat has a significant role to play in the body, however intake should still be kept low. Trans fats (often listed as hydrogenated oils) appear to be of significantly more danger again .
So whilst cholesterol rich foods such as eggs and prawns are given the “all-clear”, it isn’t an invitation to go hell-for-leather on animal food products. Saturated fat still has a role to play in altering blood lipids for the worse, despite what paleo diet advocates might suggest.
To momentarily digress, if a “paleo style” diet (lower-carb, high-fat) enables you to significantly reduce body fat, this may still be beneficial to heart health. A higher intake of fat combined with a lower intake of carbohydrates is certainly a lesser evil than a high intake of saturated fat combined with a high intake of refined carbohydrate. However this does not make it the most optimal approach. As there is evidence to suggest that weight loss on a low carbohydrate/high fat diet can still be accompanied by an increase in LDL-cholesterol .
Given such, lowering saturated fat intake is still recommended by reputable dietary guidelines. With the evidence to support the power of plants in lowering cholesterol and improving heart health, reducing intake of animal products and replacing them with whole plant foods seems an entirely rational approach [1, 6].
There is no need to forgo nutritious, cholesterol rich foods such as eggs. However substituting animal foods high in saturated fat, for plant foods high in fibre and phytosterols (such as nuts and seeds), will go a long way to improving overall heart health and reducing risk for CVD.
- Griffin, J.D. and A.H. Lichtenstein, Dietary Cholesterol and Plasma Lipoprotein Profiles: Randomized-Controlled Trials. Curr Nutr Rep, 2013. 2(4): p. 274-282.
- Hopkins, P.N., Effects of dietary cholesterol on serum cholesterol: a meta-analysis and review. Am J Clin Nutr, 1992. 55(6): p. 1060-70.
- Chang, C.L., et al., Incremental replacement of saturated fats by n-3 fatty acids in high-fat, high-cholesterol diets reduces elevated plasma lipid levels and arterial lipoprotein lipase, macrophages and atherosclerosis in LDLR-/- mice. Atherosclerosis, 2014. 234(2): p. 401-9.
- Huang, Z., et al., Trans fat intake lowers total cholesterol and high-density lipoprotein cholesterol levels without changing insulin sensitivity index in Wistar rats. Nutr Res, 2009. 29(3): p. 206-12.
- Mansoor, N., et al., Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. Br J Nutr, 2016. 115(3): p. 466-79.
- Brown, L., et al., Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr, 1999. 69(1): p. 30-42.