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Sep

2011

Fats and Cholesterol: Out with the Bad, In with the Good - What Should You Eat? - The Nutrition Source - Harvard School of Public Health

"Eat a low-fat, low-cholesterol diet" has been the mantra for healthful eating for decades. Touted as a way to lose weight and prevent or control heart disease and other chronic conditions, millions of people have followed (or, more likely, have tried to follow) this advice. Seeing a tremendous marketing opportunity, food companies re-engineered thousands of foods to be lower in fat or fat free. The low-fat approach to eating may have made a difference for the occasional individual, but as a nation it hasn't helped us control weight or become healthier. In the 1960s, fats and oils supplied Americans with about 45 percent of their calories; about 13 percent of us were obese and under 1 percent had type 2 diabetes, a serious weight-related condition. Today, Americans take in less fat, getting about 33 percent of calories from fats and oils; yet 34 percent of us are obese and 8 percent have diabetes, most with type 2 diabetes.

www.hsph.harvard.edu/...index.html

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nutrition fat cholesterol omega3 omega6 fatty acids trans fatty acids unsaturated monounsaturated polyunsaturated

in list: science

Today, Americans take in less fat, getting about 33 percent of calories from fats and oils; (1) yet 34 percent of us are obese and 8 percent have diabetes, most with type 2 diabetes. (4, 5)

Why hasn't cutting fat from the diet paid off as expected?
Bad fats, meaning trans and saturated fats, increase the risk for certain diseases. Good fats, meaning monounsaturated and polyunsaturated fats, do just the opposite. They are good for the heart and most other parts of the body.
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- Almost all foods contain some fat. Even quintessential fat-free foods like carrots and lettuce contain small amounts of this nutrient. That's a testament to how important fats are for life.
- Fat provides a terrific source of energy as well as a great depot for storing it
- It is an important part of cell membranes, helping govern what gets into cells and what comes out
- The body uses cholesterol as the starting point to make estrogen, testosterone, vitamin D, and other vital compounds
- Fats are also biologically active molecules that can influence how muscles respond to insulin's "open up for sugar" signal; different types of fats can also fire up or cool down inflammation.
- Fat and cholesterol can't dissolve in water or blood. The body gets around this basic chemistry problem by packaging fat and cholesterol into tiny, protein-covered particles called lipoproteins. Although lipoproteins can carry quite a bit of fat, they mix easily with blood and flow with it. Some of these particles are big and fluffy, others small and dense. The most important ones are low-density lipoproteins, high-density lipoproteins, and triglycerides.
- When there is too much LDL cholesterol in the blood, these particles can form deposits in the walls of the coronary arteries and other arteries throughout the body.
- narrow arteries and limit blood flow
- LDL cholesterol is often referred to as bad, or harmful, cholesterol
- High-density lipoproteins (HDL) scavenge cholesterol from the bloodstream, from LDL, and from artery walls and ferry it back to the liver for disposal. Think of HDL as the garbage trucks of the bloodstream. HDL cholesterol is often referred to as good, or protective, cholesterol.
- The types of fat in the diet determine to a large extent the amount of total and LDL cholesterol in the bloodstream
- Cholesterol in food matters, too, but not nearly as much.
- Unsaturated fats are called good fats because they can improve blood cholesterol levels, ease inflammation, stabilize heart rhythms, and play a number of other beneficial roles.
- Monounsaturated fats are found in high concentrations in canola, peanut, and olive oils; avocados; nuts such as almonds, hazelnuts, and pecans; and seeds such as pumpkin and sesame seeds.
- Polyunsaturated fats are found in high concentrations in sunflower, corn, soybean, and flaxseed oils, and also in foods such as walnuts, flax seeds, and fish. Omega-3 fats, which are fast becoming the darling of the supplement industry, are an important type of polyunsaturated fat. The body can't make these, so they must come from food. An excellent way to get omega-3 fats is by eating fish two or three times a week. Good plant sources of omega-3 fats include chia seeds (sold as Salvia), flax seeds, walnuts, and oils such as flaxseed, canola, and soybean.
- Dutch researchers conducted an analysis of 60 trials that examined the effects of carbohydrates and various fats on blood lipid levels. In trials in which polyunsaturated and monounsaturated fats were eaten in place of carbohydrates, these good fats decreased levels of harmful LDL and increased protective HDL. (10) More recently, a randomized trial known as the Optimal Macronutrient Intake Trial for Heart Health (OmniHeart) showed that replacing a carbohydrate-rich diet with one rich in unsaturated fat, predominantly monounsaturated fats, lowers blood pressure, improves lipid levels, and reduces the estimated cardiovascular risk. (11)
  
  Most people don't get enough of these healthful unsaturated fats each day
- Our bodies can make all the saturated fat we need, so we don't need to eat any of it. That's why saturated fat can be in the bad category—because we don't need to eat any of it, and it has undesirable effects in cardiovascular disease
- Seven percent of total calories or lower is a good target