Cancer
The link between fat intake and cancer is controversial. Although a study by the Harvard Medical School found no
relationship between fat intake and breast cancer, the disease occurs more frequently in countries where women have high average intakes of both total fat and saturated fat. (American women are six times more likely to develop breast cancer than Japanese women, who eat far less fat.)
Studies are mixed as to whether a high-fat diet increases the risk
of cancer of the colon, ovary, uterus, endometrium, and prostate.
Athletic Considerations
Fat (especially) and protein slow the workings of the stomach
and intestines in comparison with carbohydrate. Fatty meals before intense efforts are associated with stomach bloating and gastrointestinal distress.
Slow long-distance cycling burns mostly fat. Higher-intensity
efforts require not only fat but also the higher levels of energy provided by carbohydrate.
By analogy, one might say that high-glycemic carbohydrates are
like burning paper, medium- and low-glycemic carbohydrates are like burning wood, and fats are like burning coal.
Medium-chain triglycerides (MCTs)—partially broken down
fats—were reported by Van Zyl in
1996 to improve performance.
Promotion and marketing of these products quickly followed. Efforts to reproduce these results failed.
For more information about overall macronutrient mix
recommendations for aerobic endurance athletes, see page
47
.
Omega-3 Fatty Acids
Omega-3 fatty acids are polyunsaturated, meaning they contain
more than one double bond. They are called omega-3 fatty acids because the first double bond from the methyl end is located at the third carbon atom.
Alpha-linolenic acid is an essential omega-3 fatty acid. Humans can synthesize other needed omega-3 fatty acids from
alpha-linolenic acid, including eicosapentaenoic acid and docosahexaenoic acid.
Eicosapentaenoic acid and docosahexaenoic acid are abundant in
some fish; they are referred to as marine-derived omega-3 fatty acids. Alpha-linolenic acid is a plant-derived omega-3 fatty acid.
Linoleic acid is another essential polyunsaturated fatty acid; it is
an omega-6 fatty acid and has two double bonds.
It has been estimated that the ratio of omega-6 to omega-3 fatty
acids in the diet of early humans w
as 1:1. The ratio in the typical US
diet is about 10:1 due to increased use of vegetable oils rich in linoleic acid and declining fish consumption.
Increasing the relative amount of dietary omega-3 fatty acids may
have health benefits.
Requirements: Adequate Intake (AI)
The 2002 US Food and Nutrition Board (FNB) daily adult
adequate dietary intake levels (A
Is) for omega-3 fatty acids is 1.6
grams of alpha-linolenic acid for men and 1.1 grams of alpha-linolenic acid for women.
Nutrition for Sports, Essentials of 81
