Does a tax on the fat content of foods reduce obesity and help people to eat less fat and less saturated fat?
What is obesity?
Body mass index (BMI) is usually a useful measure to show whether people are a healthy weight for their height. A BMI of 18 to 25 shows a healthy weight, a BMI over 25 is considered overweight, and a BMI over 30 shows obesity.
Obesity is generally caused by consuming more energy (calories) than you burn off through physical activity or exercise. The body stores the excess energy as fat.
Obesity can lead to serious and life-threatening conditions, including type 2 diabetes, coronary heart disease, some types of cancer (such as breast cancer and bowel cancer), and stroke. Obesity can also affect people's quality of life (well-being).
What are fats?
Fat is essential to a healthy, balanced diet. Fats help the body to absorb some vitamins, and are a source of some fatty acids that the body cannot make. The main types of fat in foods are:
- saturated (mostly from animal products, such as meat, cow's milk, cheese, cream, and butter); and
- unsaturated (mostly found in oils from plants and fish).
Health guidelines usually recommend that people should:
- reduce the overall amount of fat they eat;
- limit the amount of saturated fats they eat; and
- eat unsaturated fats instead of saturated fats.
Why we did this Cochrane Review
Rates of overweight and obesity are increasing around the world and are a major public health issue. We wanted to know whether increasing the prices of foods that have a lot of fats or saturated fats could put people off eating them, and reduce obesity.
What did we do?
We searched for studies that looked at the effects of a tax on the fat content of foods. We were interested in how a tax affected the:
- total amount of fat, and saturated fats eaten;
- total calories eaten;
- calories eaten from all fats and saturated fats; and
- rates of overweight and obesity.
We included evidence published up to September 2019.
What we found
We found two studies from Denmark, conducted during 2011 to 2012. One looked at how a tax on some high-fat foods affected household demand for them; the other looked at information on supermarket sales for certain high-fat foods (minced beef, cream, and sour cream). They compared their results with data from before the tax started.
Both studies looked at a small number of foods that people bought, but not what foods people ate. They didn't measure how much total fat or saturated fat were eaten.
What are the results of our review?
If the amount of foods bought reflected the amount of foods eaten, then taxing the fat content of certain foods:
- might reduce the total amount of fats eaten by 41.8 grams a week for each person in a household, in one study of 2000 households; and
- might reduce the amount of saturated fats eaten (in minced beef and cream), in one study of 1293 supermarkets.
No studies measured the effect of taxing the fat content of foods on calories eaten, on obesity or overweight, or on total food sales.
How reliable are these results?
We are not confident in the results because the evidence is only from two studies; and these studies only measured a small number of foods bought, and did not measure foods eaten. One study did not report statistics about the accuracy of its results.
The results were from observational studies, in which researchers observe the effect of a factor (such as taxation) without trying to change who does, or does not, experience it. Observational studies do not give as reliable evidence as randomized controlled studies, in which the treatments people receive are decided at random.
We did not find enough reliable evidence to find out whether a tax on the fat content of foods resulted in people eating less fat, or less saturated fat.
We did not find any evidence about how a tax on the fat content of foods affected obesity or overweight.
The results of our review will change when further evidence becomes available.
Discussing the findings of this review, lead author Stefan Lhachimi said, “A tax on saturated fats could be in principle a good approach to reduce the consumption of so-called junk foods, a group of food products which is fiendishly tricky to define in legal terms. By taxing a main and unhealthy component of junk foods, i.e. saturated fat, consumption could be discouraged.” He continued, “The Danish fat tax is a lost opportunity. As an active researcher it is sad to see that the accountable authorities did not implement a thorough prospective evaluation of this game-changing policy initiative.”