Can you lower your cholesterol just by changing your diet?
Statins are used to lower cholesterol but how much can be achieved with changes to diet alone, asks Michael Mosley.
Over the many years that I've been making science documentaries I've covered a huge range of subjects, but there is one that is of particular personal interest. My family tree is riddled with heart disease and I know that, unchecked, my cholesterol scores tend to soar.
I am not alone - 60% of people in Britain have cholesterol levels that are too high and increasingly we are recommended to go on statins. Yet statins have side effects and many people are reluctant to go on a lifetime of pills.
So, for the current series of Trust Me, I'm a Doctor, we wanted to see if you could lower your cholesterol just as effectively by changing your diet.
We asked Dr Scott Harding from Kings College London to help us set up and run a small study. With his help we recruited 42 volunteers, all of whom had concerns about their cholesterol and were keen to see what they could do without taking medication.
We started by taking blood samples to look at their current levels of total cholesterol.
Cholesterol is complicated stuff. Most of it is made in the liver and then sent to the cells that need it, bound to a lipoprotein called LDL (low density lipoprotein).
LDL is often called "bad cholesterol" because high levels are associated with an increased risk of heart disease. HDL (high density lipoprotein) is known as "good cholesterol" because it carries cholesterol away from the arteries to the liver.
Current recommendations are that levels of "bad" LDL-cholesterol should be less than 3mmol/l (millimoles per litre) and "good" HDL-cholesterol more than 1mmol/l.
Once we had taken their bloods, Scott randomly allocated our volunteers into three groups. Each group was asked to modify their diet in a different way.
The first group was asked to go on a traditional low cholesterol diet. They were asked to switch from animal fats (full-fat milk, full-fat cheese, butter) to vegetable-based or low-fat options. They were asked to cut out eggs, bacon and sausages, and stick to skinless chicken.
The second group wasn't asked to give up any of the foods but were asked to eat 75g of oats a day, equivalent to three servings. Oats are full of fibre and any form of fibre - whether it is from grains, legumes (beans and lentils) or vegetables is likely to lower cholesterol by binding with fat and cholesterol in the gut and stopping it being absorbed.
The third group was asked to eat normally but to add into their diet 60g of almonds a day (two handfuls). In recent years tree nuts such as almonds, walnuts and hazelnuts have become hugely popular thanks to studies which suggest they can lower cholesterol. Tree nuts are rich in fibre and plant sterols which may delay fat and cholesterol absorption.
Clutching their diet sheets, our happy volunteers were sent off to test their new treatments for four weeks.
Rather than doing any one diet I wanted to see if combining elements of all three diets would have a bigger effect. So I cut back a bit on bacon and sausages and added into my diet the almonds and the oats.
This approach is based on something called the Portfolio diet, developed by David AJ Jenkins in Toronto. The idea is to try lots of different cholesterol-lowering approaches at once. The full Portfolio diet includes not only nuts and oats but plant sterols and soya.
Plant sterols are found in fruit, vegetables and nuts, but in low amounts. You can also get them in fortified margarines and yoghurts.
Soya products such as soy milk and soy protein enjoy a reputation as a healthy alternative to dairy, but a few years ago the European Food Safety Authority rejected claims about the benefits of soy on the grounds that most randomised controlled studies don't show an effect. Soy seems to work by inhibiting cholesterol synthesis in the liver. Amounts of 15-25g have been recommended in order to get the maximum effect.
How well does the Portfolio diet work? A study published in 2011 found that people who agreed to try the diet for six months saw an average reduction of about 13% in LDL-cholesterol. The best results were obtained by those who stuck closest to it.
- Fatty substance known as a lipid, vital for normal body functioning; mainly made by the liver but can also be found in some foods
- Carried in blood by proteins with which it combines to form lipoproteins (illustrated above) - low density lipoproteins (LDLs) carry cholesterol from liver to cells, high density lipoproteins (HDLs) carries cholesterol from cells to the liver
- If LDLs have too much cholesterol, it will build up on artery walls and increase risk of heart disease and stroke
So how did our volunteers get on? The results were not quite as expected. The first surprise was the almond eaters.
"Half the group had a positive response," Scott told me., "And one individual had an 18% reduction in their total cholesterol. On the other side of the coin some people had an adverse response. Their cholesterol actually went up, in some cases significantly."
The raised levels of cholesterol in some almond eaters balanced the falls in others. On average there was no change.
The porridge eaters and the low-animal-fat group did rather better, with an average fall in LDL-cholesterol of 10% and 13% respectively.
The biggest surprise, however, was me. My LDL cholesterol fell by an impressive 42%. This is in line with what most people experience who go on statins.
Why did I do so well? Hard to say. It could be that my combination approach (Portfolio-lite) worked better than doing things in isolation or it could be that my body responds more dramatically to a combination of oats, almonds and bacon-skipping than most people.
So the answer is yes, you can drop your cholesterol significantly through modest changes to diet, but to get as big an effect as you would through taking statins you would probably need to combine a number of different approaches.
The best advice would be to get your bloods taken before and after any dietary change to understand what works best for you.
Trust Me I'm A Doctor continues its new series on BBC Two at 20:00 BST on Wednesday 22 July - or watch on BBC iPlayer
Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.