Low-fat diet – an efficient method for rapid, targeted weight loss, or the starting point for nutrient deficiencies and other negative consequences? Low-fat eating was widely promoted some time ago as a way to lose weight and prevent cardiovascular disease. However, the scientific community is now relatively united in its view that a radical fat-free diet is particularly harmful to health and can have many negative long-term effects. There are, however, less extreme forms of the low-fat diet that may be justified at least temporarily.
What is the low-fat diet?
There are various versions of this dietary approach. In principle, it is based on the idea that a low-fat diet automatically reduces calorie intake. This assumption is based on the fact that fat is the macronutrient with the highest energy density: 1 g of fat contains 9.3 kilocalories, while carbohydrates and protein contain only 4.1 kilocalories per gram by comparison.
Furthermore, proponents of low-fat diets believe that fat makes you fat, because the equation sounds logical: fat = body fat. Since too much body fat can lead to the fatty degeneration of tissues and arteries, causing long-term health damage, and many people want to look slim, it sounds plausible to simply eat less fat for this reason. Well, both reasons given for eating less fat are understandable – but the human body and its metabolism are considerably more complex, which is why there are other dietary adjustments that are significantly more effective.
The low-fat diet can also have many health disadvantages: hormonal imbalances, a deficiency of essential fatty acids that the body needs for the stability of cell walls, the brain, and many other mechanisms, and reduced intake of fat-soluble vitamins and minerals are just a few of them. In addition, people often consume much more sugar instead of fat, which in turn has further indirect negative effects on health, body fat reduction, and overall well-being.
Low-fat diet explained: How the trend emerged – A historical look at the world of dieting
The hype surrounding the low-fat diet began in the 1990s and persisted through the years to the present day – although it is no longer as popular as it once was. At that time, rapid global developments and the industrialization of food, along with a new abundance of food, brought cardiovascular disease and obesity to the attention of doctors, nutrition experts, and the general public. Low-fat diets became increasingly well known, especially in the United States and amid Hollywood's obsession with beauty and slimness, where a new dietary craze was constantly being hyped up. The trend then quickly caught on in Europe and Germany as well.
How many grams of fat can you eat on a low-fat diet? The low-fat diet macronutrient distribution
There are various definitions within the low-fat diet rules regarding the maximum number of grams of fat that should be eaten per day. Most recommendations are based on the basic daily calorie requirement and are expressed as percentages accordingly: depending on how radical the approach is, 10–30% of the daily calorie intake may come from fat. At 30%, this would actually already be the daily amount recommended by the German Nutrition Society1. However, it should be noted that most people do not follow these guidelines, and for many, 30% already represents a reduction in fat. For an average woman with a daily requirement of 1,600 kilocalories, this would amount to 50–60 g of fat. However, the low-fat diet often aims for a much lower dietary fat target:
There is the 30-gram fat diet, in which no more than the stated 30 g of fat per day may be consumed. Those who follow the lower limit of 10% of daily calories would then consume just 15 to 20 g of fat per day. How much fat is actually consumed on this diet is therefore also a matter of interpretation. As can be seen, there are very radical forms and milder ones that are based on official health-oriented recommendations.
To get down to such a small number of grams of fat per day, dishes are prepared with little fat: lean meat is boiled instead of fried, low-fat yoghurts are consumed, and highly fatty foods such as butter, pure oils, nuts, and cream are avoided. Instead, the low-fat diet meal plan includes things such as low-fat margarine, often industrially processed low-fat and light products, more carbohydrates, fruit, and vegetables. This is also where part of the problem with the low-fat diet lies: it is usually viewed in black and white, and only the macronutrient fat is avoided. Too little attention is paid to the quality of the food and the sugar in low-fat products.
Low-fat diet: Advantages and disadvantages
If the low-fat diet is not pursued too radically and at least 30 to 40 g of fat per day is maintained, it can actually lead to faster weight loss in a short period of time. This is sometimes unavoidable for competitive athletes who need to reach the right weight for their weight class shortly before a competition, or for bodybuilders who want to reduce their body fat to a minimum. Occasionally, severely limiting dietary fat can also be beneficial for restoring intestinal health. In carb cycling, which is often used by bodybuilders and in the fitness world to achieve aesthetic goals, high-fat and high-carbohydrate days are alternated. This can also be beneficial for the metabolism, and since there are regular days with more fat, the risk of an essential fatty acid deficiency and impaired absorption of fat-soluble vitamins is low.
If the advantages are to be truly sustainable, however, this low-fat diet should never be pursued radically over the long term, meaning no more than one or two weeks at a time with a maximum of 15 to 20 g of fat per day. In addition, it must still be ensured that little sugar is consumed and that industrially processed low-fat foods are not used. Otherwise, the low-fat diet is generally not recommended, because it carries several risks and is often significantly less effective than the low-carb diet...
Low-fat or low-carb diet – which is more effective?
The article on the “Keto Diet and Ketosis” already described the low-carb diet in more detail. In that approach, very large amounts of fat are consumed daily – the opposite of the low-fat diet – and a maximum of 30–40 g of carbohydrates. Carbohydrates are not essential to the body – it can produce them itself, or use a substitute product, if they are not provided through food. This is different with fats: there are numerous essential fatty acids that the body cannot synthesize itself and that must be obtained through food. Omega-3 fatty acids, for example, are among these vital fats. The intestinal mucosa also needs the right fats to maintain its protective layer. All other cell membranes are also composed of a lipid layer.
Fats are also the basis for all steroid hormones, meaning that DHEA, testosterone, estrogen, cortisol, and vitamin D3 depend on this macronutrient. The hormonal cascade can be severely impaired by a long-term low-fat diet, which can have many negative effects – both physical and mental. A radical low-fat diet also makes a vitamin deficiency inevitable: vitamins A, K, and D are fat-soluble and cannot be absorbed without fat. More on the topic of fats can be found in the article "Why Fat Is Not the Same as Body Fat."
Conclusion on the low-fat diet
A severely low-fat diet over the long term can have dangerous health consequences and is also significantly less effective for body fat reduction goals than other dietary approaches. However, the low-fat diet can provide new positive stimuli for the metabolism as an interval solution, meaning with a low-fat week or alternating low- and high-fat days. It is also always advisable to severely reduce industrially processed fats and trans fats and instead rely on natural fats and unrefined oils.
Sources:
1 DGE: Reference values for fat. [https://www.dge.de/wissenschaft/referenzwerte/fett/?L=0; 18.02.2021].