J Am Coll Nutr 2001 Feb; 20(1):5-19

Types of dietary fat and risk of coronary heart disease: a critical review.

Hu FB, Manson JE, Willett WC.

During the past several decades, reduction in fat intake has been the main focus of national dietary recommendations to decrease risk of coronary heart disease (CHD). Several lines of evidence. however, have indicated that types of fat have a more important role in determining risk of CHD than total amount of fat in the diet. Metabolic studies have long established that the type of fat, but not total amount of fat, predicts serum cholesterol levels. In addition, results from epidemiologic studies and controlled clinical trials have indicated that replacing saturated fat with unsaturated fat is more effective in lowering risk of CHD than simply reducing total fat consumption. Moreover, prospective cohort studies and secondary prevention trials have provided strong evidence that an increasing intake of n-3 fatty acids from fish or plant sources substantially lowers risk of cardiovascular mortality. In this article, we review evidence from epidemiologic studies and dietary intervention trials addressing the relationship between dietary fat intake and risk of CHD, with a particular emphasis on different major types of fat, n-3 fatty acids and the optimal balance between n-3 and n-6 fatty acids. We also discuss the implications of the available evidence in the context of current dietary recommendations.

Key teaching points:
1. In the past several decades, reduction in fat intake has been the main focus of national dietary recommendations to lower risk of coronary heart disease (CHD).
2. Metabolic studies have long established that the type of fat, but not total amount of fat, predicts serum cholesterol levels.
3. Results from epidemiologic studies and controlled clinical trials have indicated that replacing saturated fat with unsaturated fat is more effective in lowering risk of CHD than simply reducing total fat consumption.
4. Prospective cohort studies and secondary prevention trials have provided strong evidence that a higher intake of n-3 fatty acids from fish or plant sources lowers risk of CHD.
5. Recent national dietary guidelines have shifted the emphasis from total fat reduction to distinguishing different types of fat.

INTRODUCTION
During the past several decades, reduction in fat intake has been the main focus of national dietary recommendations. In the public’s mind, the word “dietary fat” has become synonymous with obesity and heart disease, whereas the words “low-fat” and “fat-free” have become synonymous with heart health. In response to the low-fat campaign, the food industry has produced numerous commercial products labeled as “low-fat” or “fat-free,” but with high amounts of refined carbohydrates and sugar. Ironically, while dietary fat intake as percentage of energy intake has declined in the US over the years, total caloric intake has not declined, and the prevalence of obesity and type 2 diabetes has grown dramatically.
It is now increasingly recognized that the low-fat campaign has been based on little scientific evidence and may have caused unintended health consequences. It is also increasingly appreciated that different types of fats have different health effects. …
MAJOR TYPES OF DIETARY FAT
A higher intake of total and saturated fat is widely believed to contribute to the development of CHD. This belief is largely based on ecological studies relating dietary intake of saturated fat and rates of CHD. In the Seven Countries Study, intake of saturated fat as a percentage of calories was strongly correlated with coronary death rates across 16 defined populations in seven countries. Interestingly, the correlation between the percentage of energy from total fat and CHD incidence was much weaker. Indeed, the regions with the highest CHD rate (Finland) and the lowest rate (Crete) had the same amount of total fat intake, at about 40% of energy which was the highest among the 16 populations….
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A major purported benefit of a low-fat diet is weight loss. But long-term clinical trials have not provided convincing evidence that reducing dietary fat can lead to substantial weight loss. On the contrary, there is some evidence that a diet containing a high amount of refined carbohydrates may increase hunger and promote overeating, which can lead to weight gain and obesity. It is now generally agreed that total energy intake, whether from fat or carbohydrate, relative to energy expenditure, is a more important determinant of body weight than dietary fat per se.
It has been increasingly recognized that the widely promoted low-fat concept is too simplistic and not compatible with available scientific data. ….
However, due to the campaign against total fat over the years, the belief that “fat is bad” has been strong and widespread. Thus, great educational efforts are needed to communicate nutritional messages about the health effects of different types of fat to the public and to translate current dietary recommendations into dietary practice as well.