High cholesterol: Does reducing the amount of fat in your diet help?

There are two main different types of fats in our diets, called saturated and unsaturated fats. Larger amounts of saturated fats are considered to be bad for your heart and blood vessels. These fats increase the amount of LDL cholesterol in your blood.

Saturated fats are mainly found in animal food products, especially in

• meat (mainly fatty meats like pork),
• butter and lard,
• cheese (particularly hard cheeses) and
• cream and related food products, such as sour cream.

Unsaturated fats are mainly found in fatty fish and vegetable fats and plant-based foods, including

• salmon, tuna and mackerel,
• vegetable oils, such as sunflower oil or olive oil,
• nuts and seeds, and
• avocados.

The researchers analyzed the results of 48 randomized controlled trials involving more than 65,000 participants. They compared two different approaches to eating fats. In some studies, the participants were asked to reduce the overall amount of fat in their diet, and in other studies they were asked to replace saturated fats with unsaturated fats as much as possible.

One of the main differences between the studies was that they used different interventions to help the participants change their diets. In some studies, people had nutrition and cooking classes, were given shopping tips or took part in practical exercises. But in many studies the participants were also provided with certain foods – for example, they bought their foods in special shops or were given free products such as margarine spreads or oils. These differences make it quite difficult to compare the results of the individual studies.

Overall, the studies suggest that reducing the amount of saturated fats in your diet lowers your risk of cardiovascular disease. Here it probably doesn’t make a difference whether you reduce the overall amount of fat in your diet or try to replace saturated fats with unsaturated fats. Expressed in numbers, when the researchers analyzed the results of all of the studies together, this is what they found:

• Without dietary changes: 77 out of 1,000 people who didn't change their diet developed cardiovascular disease.
• With dietary changes: 72 out of 1,000 people who were encouraged to eat less saturated fat developed cardiovascular disease.

In other words, interventions that help people to reduce the amount of saturated fats in their diet prevented cardiovascular disease in 5 out of 1,000 people.

But this difference was only seen in studies that lasted longer than two years. So people probably have to change their diet permanently if they want to make a positive difference to their health.

The overall results of the analysis can only provide a rough indication of the effect of changing your diet, though, because the results of the individual studies varied greatly. Many different factors can influence how successful dietary changes will be. For example, men might benefit more from changing their diet because they have a higher risk of cardiovascular disease to begin with.