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Is The Low Fat Diet Dead Yet?

Caitlin Hosmer, MS, RD, LDN, Brigham and Women's Hospital

Despite all of the scientific evidence about the health benefits of some kinds of fat - even in weight loss - there are still a lot of people trying to lose weight primarily by avoiding all kinds of fat. We would like to remind you of some basic principles for sniffing out a fad "diet": food-specific diets rely on the myth that some foods have special properties that can cause weight loss or gain. These diets don't teach healthful eating habits; therefore, you won't stick with them. Sooner or later, you'll have a taste for something else - anything that is not among the foods you've been "allowed" on the diet.

The truth is that any diet that encourages fewer calories, whether they be from carbohydrates or fats, will produce weight loss. This general assumption was verified in a research study done by colleagues here at BWH. Published in the New England Journal of Medicine in 2009, the study showed that diets ranging in fat, protein, and carbohydrate are successful at promoting weight loss. The key is finding an eating strategy that is healthy, enjoyable and long-lasting.

It's not as catchy, but moderation is still an appropriate message:

Too Little Fat

Following a diet intentionally low in fat usually results in fat being replaced by excessive carbohydrate intake. Low fat versions of grain foods (crackers, cookies, pastries) have additional sugar and/or salt added to compensate for the reduction in flavor (flavor compounds are primarily fat-soluble). Because of the processing necessary to remove the fats and make a palatable product, these foods end up being very nutrient poor. In addition, studies have shown that after eating refined carbohydrate foods (such as white bread, white rice, pasta, rice cakes, etc.) there is a rapid rise in blood sugar. The body then produces insulin to take care of the elevated blood sugar. After the insulin works on reducing the level, the blood sugar decreases (often times below baseline). A low blood sugar can increase hunger with the result of more food intake.(Low fat dairy products and leaner meats are still a good choice because they are lower in saturated fat and contain protein.)

Too much saturated and trans fat

On the other end of the spectrum, those touting the practicality of the Atkin's Diet emphasize the pleasure of eating large steaks, egg and sausage breakfasts, and plenty of cheese. One of the biggest beefs (no pun intended) about this diet is not the quantity of fat - natives from Crete eating a Mediterranean diet ate as much as 40% of their calories from fat - but rather the quality of the fat. Those promoting this diet would be better off encouraging people to cook with olive oil, add avocados to salad and eat nuts in between meals to curb hunger and prevent overeating (while limiting the most refined, "empty calorie" carbohydrates). Nobody has disproved the fact that replacing saturated fat with unsaturated fat is better for your heart health.

Also watch out for trans fat. These fats raise the bad (LDL) cholesterol and lower the good (HDL) cholesterol. They are found in margarines, foods containing "partially hydrogenated vegetable oil" and most fried foods (french fries, donuts, etc.).

Bottom Line:

  • Healthy fats can be part of a healthy weight and diet, but watch the portions
    • Re-acquaint yourself with nuts, seeds and nut and seed butters (peanut butter, almond butter,tahini-natural versions)
    • Add avocados to salads and sandwiches, enjoy a dip of guacamole once in a while
    • Add fatty fish to your menu several times/week (fresh or canned salmon, sardines, mackerel, herring, albacore tuna)
    • Choose olive oil for cooking and canola oil for baking
  • Eat more colorful vegetables, fresh or frozen
  • Eat smaller servings of nutrient poor, low fat carbohydrates like crackers, white bread, white rice, white potatoes; and fewer foods rich with bad fats and sugar such as cakes, pastries and deep fried foods.

Weight loss is still an energy equation. Most women need to cut back on their portions and expend more energy.


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