Cholesterol is transported in the blood in complexes called lipoproteins. High-density lipoproteins (HDLs) tend to remove cholesterol from the tissues to the liver for excretion. Low-density lipoproteins (LDLs) are more likely to deposit cholesterol in damaged areas of blood vessels and lead to the formation of atherosclerotic plaques. High levels of LDL cholesterol can lead to heart disease, whereas high levels of HDL cholesterol can protect against heart disease.

The evidence on plant-based diets

Vegetables in a market

The evidence on plant-based diets

Many believe that eating a plant-based diet is healthier and better for the environment. They’re right – but there are some exceptions

In the West, being a vegetarian or vegan is usually seen as a diet choice, while in some parts of the world it is a result of simple poverty: people may be unable to get the nutrients they need from meat or elsewhere. In other cases, the decision not to eat meat may have religious or cultural significance.

It is often said that India is a vegetarian country, but most of the population do in fact eat meat and there is a complex mix of socioeconomic, political, religious and cultural reasons why around a third of them do not. Some claim that abstaining from meat originally became socially acceptable because at times in India’s past it was too scarce or too expensive for many families to afford.

Assuming vegetarians have access to a wide range of other foods, there is little reason to suspect that a diet that without meat or fish should be less nutritious overall, although there are likely to be differences in the exact balance of nutrients. For example, while many people complain that meat-free diets lack iron, research suggests that the risk of iron deficiency is similar across meat-eaters, vegetarians and vegans, perhaps because non-meat-eaters consume more fruit and vegetables containing vitamin C, which helps our bodies absorb iron.

Some also question whether it’s possible to be in peak physical condition without eating meat, but some reassurance may come from remembering that Carl Lewis broke the world record for the 100-metre sprint while following a vegan diet.

Lower in saturated fat – but lower in omega-3s too

Vegetarian diets tend to be lower in saturated fats, which come from animal products and are associated with higher levels of ‘bad’ LDL cholesterol, the type that causes our arteries to get blocked up (see our article ‘Is fat bad?’ for more on ‘good’ and ‘bad’ cholesterol). On average, vegans also have a lower risk of heart disease due to lower blood pressure.

However, there is one particular type of fatty acid that is good for our health and is difficult to get if you are strictly vegetarian. Omega-3 long-chain polyunsaturates – often referred to as ‘fish oils’ – are made by algae and help to reduce our risk of cardiovascular disease, but humans get most of theirs from the oily fish that feed on these algae.

It could now be possible to engineer plants to produce these oils. Scientists at the Rothamsted Research Institute in Hertfordshire, UK, are testing a version of the cabbage family plant Camelina that has been given algal genes to enable it to produce the necessary fatty acids.

Why it’s greener to eat greens

Some people choose to be vegetarian for environmental reasons, as meat has a larger environmental ‘footprint’ than crops. This is related to the greater amount of energy needed to grow fodder for livestock and the amount of harmful emissions produced. By some estimates, livestock account for 15 per cent of global greenhouse emissions.

The authors of one 2015 study calculated that removing meat and fish from the diet of the average Dutch woman would reduce the environmental impact of her diet by 21 per cent and that this impact could be reduced by a further 9 per cent by adopting a healthy vegan diet. Even eating a little bit less meat, rather than becoming completely vegetarian, would have positive environmental consequences.

However, according to a 2016 survey, many people did not believe that reducing meat consumption would have a large impact or thought that it would not be worthwhile unless there was a wider societal change.

Lead image:

Moyan Brenn/Flickr CC BY

References

About this resource

This resource was first published in ‘Plants’ in May 2016.

Topics:
Ecology and environment, Health, infection and disease
Issue:
Plants
Education levels:
16–19, Continuing professional development

Close-up on cholesterol

Cholesterol molecule diagram

Close-up on cholesterol

Cholesterol is a necessary part of all of us

Our notion of cholesterol as bad is overly simplistic. For example, it helps regulate the fluidity of cell membranes. And, in the context of health, often when we say ‘cholesterol’, we’re actually referring to two cholesterol transporters found in the blood: high-density and low-density lipoprotein, otherwise known as HDL (‘good’) and LDL (‘bad’) cholesterol. (For more, see our animation on cholesterol transport.)

While further subdivisions of LDL cholesterol do make the picture more complex, raised levels of LDL cholesterol are generally associated with an increased risk of heart disease.

According to most sources, it is not eating high-cholesterol foods, such as eggs, that drives up our blood cholesterol levels, but eating foods that are high in saturated fats. This is because our livers turn saturated fats like those in cakes and pastries into LDL cholesterol in the blood.

The past few years have seen continued questioning of dietary guidance on saturated fats and cholesterol. However, a 2015 study based on changing the diets of 195 people for 16 weeks showed that replacing saturated fats with unsaturated fats reduced LDL cholesterol levels.

Our cholesterol levels are not determined only by what we eat but also by the genes we inherit from our parents. About 1 in 500 people have an inherited condition called familial hypercholesterolaemia, which means they have high cholesterol from birth – whereas in 499 out of 500 people, cholesterol levels don’t get higher until they get older.

Lead image:

Cholesterol molecule diagram.

‘Big Picture: Fat’ (2015)

References

Downloadable resources

About this resource

This resource was first published in ‘Fat’ in December 2015.

Topics:
Cell biology, Health, infection and disease
Issue:
Fat
Education levels:
16–19, Continuing professional development