Chapter Introduction

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6

THE LIPIDS

The Skinny on Fat HOW NATIVE GREENLANDERS WITH A PASSION FOR SEAL BLUBBER SHOWED THE WORLD THAT NOT ALL LIPIDS ARE CREATED EQUAL.

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LEARNING OBJECTIVES

  • Identify the four major categories of dietary lipids (Infographic 6.1)

  • Describe the structural differences between saturated, monounsaturated, and polyunsaturated fats (Infographic 6.2)

  • Identify the types of foods that are rich in monounsaturated fat, polyunsaturated fat, and saturated fat (Infographic 6.3)

  • Name two roles of phospholipids in the body (Infographic 6.4)

  • Describe the process of lipid digestion and explain how emulsification assists in the process (Infographic 6.5)

  • List the four major lipoproteins and describe their functions in the transport of lipids (Infographic 6.6 and Infographic 6.7)

  • Identify the two essential fatty acids, their primary structural difference, and food sources of each in the diet (Infographic 6.8)

  • Describe the Acceptable Macronutrient Distribution Range for lipids and how to use a Nutrition Facts Panel to evaluate a food's fat content (Infographic 6.9)

  • Describe sources of saturated fat in the U.S. diet (Infographic 6.10)

Even in the summer, Greenland is cold. The first time Jørn Dyerberg visited, as a young doctor in 1970, the temperature hovered around 40 degrees Fahrenheit in mid-August; on other trips, such as in April, the thermometer would drop below zero.

But Dyerberg was not deterred by the weather—he had traveled to one of the coldest places on Earth for a mission. He was there to understand why native Greenlanders—the Inuit—were much less likely to die of heart disease than similarly aged people living in Denmark (of which Greenland was a colony at the time), despite eating a high-fat diet rich in seal blubber and fatty fish.

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It was a mystery. At the time, research evidence showed that high-fat diets were associated with an increase in blood cholesterol levels, leading to numerous health problems—in particular, heart disease. This made fat public enemy number one, as heart disease was the largest killer in Denmark, the United States, and many other countries. The popularity of low-fat diets, which emphasize carbohydrates and allow fats only sparingly, was on the rise.

DIETARY FAT compound found in plant and animal foods that serves as an important energy source, and, among other functions, is necessary for absorption and transport of fat-soluble vitamins

But the relationship between dietary fat intake and health was not always consistent. Some populations—such as the Greeks, who followed a Mediterranean diet (to learn more about the Mediterranean diet and its benefits see Chapter 9)—ate relatively large amounts of fat, but had low rates of heart disease. In 1969, the head of Dyerberg’s hospital, Hans Olaf Bang, read an article about the Inuit, who ate regular lunches of raw, slippery seal organs that were chock full of fat and cholesterol, but typically died of infections such as tuberculosis, rarely of heart disease.

Lipids researcher, Jørn Dyerberg, Professor Emeritus, Department of Human Nutrition, University of Copenhagen

At the time, Dyerberg was 32 years old and working on his PhD, investigating a new way to screen blood for different types of fats. When Bang asked him to come to Greenland to collect blood samples from the Inuit to see what was going on, he jumped at the chance.

After collecting blood samples from 130 adults, Dyerberg and Bang ran the blood through a machine that analyzed its lipid content. They saw that, despite their high-fat diet, Inuit’s levels of all blood lipids were lower than those found in Danish adults. But there was one group of lipids that was found in much higher amounts in Inuit adults. This finding contradicted everything experts believed at the time—that the more lipids you had in your blood, the higher your risk of heart disease.

The Inuit blood profile couldn’t be the result of genetics, the researchers knew—whenever Inuit adults moved to Denmark and began eating a diet typical of that nation, their blood lipids looked like those of the average Dane.

The researchers were puzzled. “We knew high intake of dietary fat increases cholesterol,” says Dyerberg. “So why did the Inuit have such a healthy profile?”

Clearly, the role of dietary fat in the body was more complicated than many believed.