Losing weight with low-fat diet
Generally about fat, fatty foods, weight and disease
Fat is very energy-rich (fat contains more than twice as much energy per gram as carbohydrates). It has been considered for several decades that the fat content of food affects the following:
- Blood lipids – it has long been considered that fatty foods (especially high content of saturated fats) lead to the fact that blood fats become higher and, accordingly, increase the risk of cardiovascular disease.
- Overweight and obesity – It has long been considered that fatty foods cause gaining weight.
Therefore, authorities and the majority of the research community have recommended that people eat food where a maximum of 30% of the energy comes from fat. The purpose of this is therefore to limit our intake of fat so that we (1) do not get high blood lipids, and (2) do not gain weight. Unfortunately, all this turned out to be wrong, which we compiled in the chapter Fats and carbohydrates impact on blood lipids, weight and mortality.
Low-fat diet – even less fat
The question is whether low-fat diet (ie, food with a very low content of fat) is effective for losing weight. Several variants of low-fat diets have been tested over the years and the effect on weight loss has been evaluated. The vast majority of variants usually means that anything between 18 -30% of the energy should come from fat. Because fat is very energy-rich, low-fat food means that you have to eat a lot more carbohydrates and protein to (1) consume enough calories and (2) be satisfied. Many people who eat low-fat foods actually experience that they become more saturated, and this is explained by the fact that they simply eaten more proteins (protein is the most saturating nutrient). 9
The energy contained in fat is stored as effectively in the body as the energy contained in carbohydrates. There is no evidence that the body’s ability to store the energy of carbohydrates and fats differs. 10.
Fortunately, a large number of studies (of high quality) have been carried out to examine whether low-fat food is effective for losing weight. Science in this area is quite robust and the following can be said:
- In 2001, Astrup and colleagues summarised the knowledge about low-fat diets by merging 13 studies. It was reported that low-fat foods gave 2.5 kg of weight loss. More precisely, it was said that for every 1% reduction in the fat content of the food you lose on average 370 grams (0.37 kg). This means that a person with BMI 30 who reduces fat intake by 10% is estimated to lose 4.4 kg. 11
- In 2004, Avenell and colleagues reported a summary of the clinical trials that were published at the time. It concluded that a low-fat diet results in a weight loss of 5.4 kg after 12 months and 3.6 kg after 3 years. A reduction in the risk of diabetes and high blood pressure (hypertension) was also observed.
- The risk of developing diabetes has been reported to decrease by 50% with a low-fat diet, according to Lindströöm and colleagues. 12
- A meta-analysis of 28 short clinical trials showed that 10% reduced energy intake from fat leads to a weight loss of 16 g per day. Based on this, it was estimated that it is possible to lose 8.8 kg in 18 months and 23.4 kg in 4 years. Unfortunately, these calculations were not correct because follow-up after 12 to 24 months showed that weight loss was almost negligible in the long term. 13
- I Women’s Health Initiative (WHI), which was also a clinical trial involving 49 thousand women, found that low-fat food (fat) was 20% of the energy intake) could not lead to long-term weight loss despite the fact that a low-fat food was also guided by a dietician. 14
Eating less fat is not a good method for losing weight. This is due to the fact that the fat of food is simply not the cause of excess weight and obesity. Anyone who wants to read about this in detail can botanise in Willet’s resume. 15 In addition, two things should be mentioned:
First of all, many studies with low-fat diet have also meant that participants were instructed to eat less food (fewer calories per day). This means that you have actually tried two things at once: less fat and fewer calories. This, in turn, means that part of the positive effect can actually be explained by the calorie restriction. Since then, low-fat foods (which were also low-calorie) were compared to Mediterranean and low-carbohydrate diet (LCHF of Atkins type) and it was done in a very well done study, where the results were as follows:
As shown in this study (Shai et al, NEJM, 2008), low-fat diet (with calorie restriction) was the worst in terms of weight loss.
Low-fat diet and risk of cardiovascular disease (heart attack, stroke, coronary heart disease)
Of course, one has always been interested in how the fat content of food (especially saturated fats) affects the risk of cardiovascular disease (coronary heart disease, stroke, heart attack). Even today (2017), a heart attack is the single most common cause of death in Sweden and the rest of the world. For over 60 years, it has been considered that the fat content of food, especially the amount of saturated fats, affects the risk of coronary heart disease. Today, however, we know that this was probably one of the greatest fathers of medical science. This theory (that the amount of fat in food has a tangible impact on the risk of coronary heart disease) turns out to be wrong only 60 years later.
A very well done study on this topic is the Womens Health Initiative (WHI), which saw that limiting the fat content of food did not affect the risk of cardiovascular disease. 16 In addition, it was found that HDL cholesterol (“good cholesterol”), triglycerides, blood sugar and insulin were not affected by eat less fat. Thus, there was no beneficial effect of eating less fat in this large and well-done study. This topic is something we discuss in detail in the chapter: Fat and carbohydrates impact on blood lipids, weight and mortality.