For many decades now, health authorities have recommended a low-fat diet.

This recommendation has been widely accepted in the mainstream medical community.

Although recent studies have raised some questions about the validity of these guidelines, most health authorities have not changed their position.

The issue is still controversial and the guidelines remain largely unchanged, even though their scientific foundation has weakened (1, 2).

So are low-fat diets truly effective at preventing heart disease or promoting weight loss? This article sums up the evidence.

Do Low-Fat Diets Work

The standard low-fat diet recommended by health authorities contains less than 30% of daily calories from fat.

Very low-fat diets generally provide 10–15% (or less) of total calories from fat.

Additionally, many health guidelines recommend that the daily calorie contribution of saturated fat should not exceed 7–10%.

Most studies investigating low-fat diets seem to follow these definitions.

Summary The low-fat diet generally provides less than 30% of total calories from fat, whereas very low-fat diets provide less than 10–15%.

Low-fat diets are often recommended for people who need to lose weight.

The main reason behind this recommendation is that fat provides a greater number of calories per gram compared to the other major nutrients, protein and carbs.

Fat provides roughly 9 calories per gram, whereas protein and carbs provide only 4 calories per gram.

Studies show that people who reduce their calorie intake by eating less fat lose weight. Although the weight loss is small, on average, it is considered relevant for health (3).

But how effective is a low-fat diet compared to a low-carb diet?

Low-carb diets are usually high in both protein and fat.

When food intake is closely monitored and controlled, low-fat diets seem equally as effective for weight loss as low-carb diets.

At least, these were the results of a small study in 19 obese adults who spent two weeks in a metabolic ward, which is a highly controlled lab environment (4).

However, the study period was short and the environment didn’t reflect a real-life situation.

Studies in free-living people generally agree that low-fat diets are not as effective as low-carb diets (5, 6, 7).

The reason for this inconsistency is unclear, but the most likely explanation is that low-carb diets are usually associated with greater dietary quality.

They tend to focus on whole foods, such as vegetables, eggs, meat and fish. They also encourage skipping most junk foods, which are usually high in refined carbs or added sugar.

Additionally, low-carb diets based on whole foods tend to be higher in both fiber and protein than low-fat diets.

A successful low-carb diet may promote weight loss in the following ways:

  • Lowers calorie intake: A high protein intake decreases calorie intake by suppressing appetite and increasing the number of calories burned (8).
  • Increases fullness: A high intake of certain types of fiber may reduce calorie intake by increasing fullness (9).
  • Fights cravings: Low-carb diets may suppress carb and sugar cravings (10).

Simply put, low-carb diets work because they promote a healthier diet.

In contrast, going on a low-fat diet without emphasizing food quality may lead to an increased intake of junk foods high in added sugar and refined carbs.

Summary Low-fat and low-carb diets are equally effective for weight loss in highly controlled situations. However, in free-living obese people, low-fat diets tend to be less effective than low-carb diets.

The low-fat guidelines were first published in 1977. Since then, many of the major health organizations have not changed their position.

The introduction of the low-fat guidelines seems to have marked the beginning of the obesity epidemic. The following picture speaks more than a thousand words:

Of course, many things were changing in society at the time and this graph does not prove that the guidelines caused the obesity epidemic.

However, I personally find it plausible that demonizing fat and giving refined carbs and sugar the green light may have contributed to it.

When consumers started believing that fat was the root of all evil, all kinds of low-fat junk foods flooded the market.

Many of these foods were loaded with refined carbs, sugar and trans fats, which are associated with heart disease, diabetes, obesity and all those diseases the low-fat diet was meant to treat (11, 12, 13).

Summary The low-fat guidelines were first published in 1977. The obesity epidemic started around the same time, but it’s unclear whether the two are connected.

When the low-fat guidelines were conceived, scientists believed that saturated fat was a significant cause of heart disease.

This idea shaped the dietary recommendations of the following decades. It explains why health organizations started discouraging people from eating foods high in saturated fat, such as eggs, fatty meat and full-fat dairy.

The guidelines were based on weak evidence at the time and not all scientists agreed. They warned that advocating for a low-fat diet could have unforeseen consequences.

Today, high-quality research suggests that saturated fat is not the villain it was made out to be. Several recent studies indicate there is no significant link between saturated fat and heart disease (14, 15).

However, replacing saturated fats with polyunsaturated fats may have benefits for heart health, probably because of their anti-inflammatory effects (16).

But the standard low-fat diet doesn’t only recommend reduced saturated fat intake. The guidelines also advise people to restrict their fat intake to less than 30% of their total calorie intake.

A number of studies show that lowering overall fat intake doesn’t improve heart health (1, 17, 18, 19).

Eating too little fat may even adversely affect risk factors for heart disease.

LDL cholesterol is often referred to as the "bad" cholesterol. However, this is only half true. The size of the LDL particles is also important.

The more small particles you have, the greater your risk of heart disease. If the particles are mostly large, then your heart disease risk is low (20, 21, 22, 23, 24).

The thing with low-fat diets is that they can actually change the LDL from the harmless large particles to the harmful, artery-clogging small, dense LDL (24, 25, 26).

Some studies also show that low-fat diets can reduce HDL “the good” cholesterol and raise blood triglycerides, another important risk factor (27, 28, 29).

Summary Low-fat diets may adversely affect levels of blood lipids, LDL pattern, HDL and triglycerides, potentially raising the risk of heart disease.

The low-fat guidelines introduced in 1977 were not based on solid evidence.

While recent studies have weakened their scientific foundation even further, the debate continues.

One thing is clear. Eating less fat is not always the best way to lose weight. Low-carb diets tend to be more effective for most people.

The association of fat with heart disease is more controversial and complex. Overall, cutting your fat intake is not likely to reduce your risk of heart disease.

Rather than worrying about your total fat intake, focus on improving the quality of your diet. Eating more whole foods and healthy fats is a good way to start.