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Genes + Fatty Diets = Obesity Risk
10/15/2009
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One in five people carry genes that promote extra pounds when they eat excess fat; Solutions can help all avoid obesity

by Craig Weatherby


About four in 10 Americans carry the “fat mass and obesity-associated gene”FTO for shortand it does them little harm.


But nearly one in five Americans (17 percent) carry two copies of the FTO gene, and this genetic variant is making them fat.


Compared to people without the FTO geneor with just one copypeople with two copies of the FTO gene are two and a half times more likely to become obese.


Previous research found that exercise blunts the obesity-promoting effects of having two copies of the FTO gene (Andreasen CH et al. 2007).


Now, a new study from Sweden suggests that people who carry the double-FTO gene variant can also reduce their risk of obesity by limiting the percentage of dietary calories they get from fat.


At this point, you may question the practical value of these findings, since few of us know whether we carry this unfortunate trait.


The answer is simple. Because each of us stands a one-in-five chance of having the FTO variant, it’s smart to assume that you do, and act on the new findings.


In addition, fats contain more than twice as many calories per gram (9) as carbohydrates and proteins do (4 calories).


Because an ounce of fat is more than twice as caloric as an ounce of carbs or protein, it is easier to cut out excess calories by limiting fat intake than by restricting intake of sugars, starches, and proteins.


However, as we'll explain, it is also unwise and unproductive to cut fat intake as low as some prominent doctors suggest.


Swedish study shows how to blunt genetic influences on weight gain

The findings of the new study, from Sweden’s Lund University, suggest that moderating fat intake and exercising more can neutralize the weight-promoting effects of the FTO variant carried by about one in five Americans.


Researchers analyzed information from 4,839 participants in the Malmö (Sweden) Diet and Cancer study, including their FTO genetic profiles, body mass indices (BMI), activity levels, and diets (Sonestedt E et al. 2009).


And the findings among people with the FTO variant were instructive:

  • People were not more likely to be obese if their carbohydrate calorie intake (as a percentage of their total calorie intake) was higher than average.
  • But those whose fat calorie intakes were higher than average (as a percentage of their total calorie intake) were more likely to be obese. And, as found in prior research, that tendency was exacerbated by sedentary lifestyles.

As the Swedes concluded, “Our results indicate that high-fat diets and low physical activity levels may accentuate the susceptibility to obesity [created] by the FTO [gene] variant.”


It isn’t necessary for people with the FTO variant to go on a very-low-fat diet such as the Ornish plan, because the Swedish results show that they had to eat more fat (as a percentage of total calorie intake) than the average American in order for the trait to make them obese.


The USDA estimates that the average American gets just over one-third of their daily calories (35 percent) from fat.


And according to lead author Emily Sonestedt, “For those who ate a diet where less than 41 percent of the energy consumed came from fat, obesity was no more common in spite of the inherited risk” (LU 2009).


She went on to make a key point: “This shows that we are not slaves to our genes. Even if we are born with an inherited predisposition to obesity, life style is important” (LU 2009).


Gene variant also disrupts satiety signals

Carriers of the FTO variant face a greater challenge than others when it comes to limiting their fat intake.


This is because the FTO variant affects the hypothalamusthe part of the brain that regulates appetite and satietyand the FTO gene variant has been linked to increased calorie intake… especially fat calories.


In other words, the FTO variant makes the brain insensitive to fat intake, causing people to eat more and more in an attempt to satisfy their desire for fat.


Sonestedt noted that compared to their peers without the FTO variant, people who carry the pair will eat more fat before they start to feel full… and this “satiety disability” that leads to weight gain.


So, while people with the FTO variant can avoid obesity by keeping their fat intake at or below the American average (about one-third of calories), it is hard for them to resist the genetically “hard-wired” desire to keep eating fat even when they’ve already consumed plenty of it.


Americans eat more calories, with fat and carbs leading the excess

In its most recent Agriculture Fact Book (2001-2002) the USDA estimated that in 2000, the average American consumed just under 2,700 calories a day.


And between 1970 and 2000, average daily calorie intake among Americans increased by 24.5 percent, or about 530 calories.


That 24.5 percent increase in daily calorie intake broke down as follows:

  • Grains (mainly white flour) contributed 9.5 percentage points
  • Added fats (i.e., fats other than those found in whole foods) contributed 9 percentage points
  • Added sugars contributed 4.7 percentage points
  • Fruits and vegetables together contributed only 1.5 percentage points
  • Meats and nuts together contributed just 1 percentage point

Interestingly, calorie intake from dairy products and eggs dropped by 1.5 percentage points… possibly due to increasing popularity of low- and no-fat milk and dairy.


Some nutritionistsled by Dean Ornish, M.D.suggest reducing fat calories to 10 to 15 percent of overall calorie intake to forestall and reverse cardiovascular disease.


But there is little evidence that this extreme approach is healthful over the long term, or helps to reduce obesity… except of course among carriers of the double FTO gene variant.


And extremely low-fat diets run the risk of starving the body of essential fatty acids, including omega-3s.


The most recent Dietary Guidelines for Americans offers this research-based advice (USDA 2005):

  • “[Adults should] Keep total fat intake between 20 to 35 percent of calories, with most fats coming from sources of polyunsaturated and monounsaturated fatty acids, such as fish, nuts, and vegetable oils.
  • “Keep total fat intake between 30 to 35 percent of calories for children 2 to 3 years of age and between 25 to 35 percent of calories for children and adolescents 4 to 18 years of age, with most fats coming from sources of polyunsaturated and monounsaturated fatty acids, such as fish, nuts, and vegetable oils.
  • “A high intake of fat (greater than 35 percent of calories)… makes it more difficult to avoid consuming excess calories. A low intake of fats and oils (less than 20 percent of calories) increases the risk of inadequate intakes of vitamin E and of essential fatty acids and may contribute to unfavorable changes in high-density lipoprotein (HDL) blood cholesterol and triglycerides.
  • “Evidence suggests that consuming approximately two servings of fish per week (approximately 8 ounces total) may reduce the risk of mortality from coronary heart disease and that consuming [the omega-3 fats] EPA and DHA may reduce the risk of mortality from cardiovascular disease in people who have already experienced a cardiac event.”

We should note that most Americans consume far too many omega-6 essential polyunsaturated fats, simply because they predominate in the vegetable oils (soy, corn, cottonseed, sunflower, and safflower) commonly found in dressings, sauces, and prepared, takeout, and packaged foods.


They also consume far too few omega-3s and, this “omega-imbalance” appears to raise the risks of cancer and various inflammatory conditions. We need omega-6s… just not as many.


Clearly, more research is needed on the FTO and other obesity-related genes, as well as the effects of various foods and diets, before we can fully understand the interactions between heredity, lifestyle, and weight gain or loss.



Sources

  • Andreasen CH, Stender-Petersen KL, Mogensen MS, Torekov SS, Wegner L, Andersen G, Nielsen AL, Albrechtsen A, Borch-Johnsen K, Rasmussen SS, Clausen JO, Sandbaek A, Lauritzen T, Hansen L, Jørgensen T, Pedersen O, Hansen T. Low physical activity accentuates the effect of the FTO rs9939609 polymorphism on body fat accumulation. Diabetes. 2008 Jan;57(1):95-101. Epub 2007 Oct 17.
  • Lund University (LU). Food habits are more important than the most important obesity risk gene. Accessed online at http://www.ludc.med.lu.se/activities/news-and-press-releases/food-habits-are-more-important-than-the-most-important-obesity-risk-gene/
  • Sonestedt E, Roos C, Gullberg B, Ericson U, Wirfält E, Orho-Melander M. Fat and carbohydrate intake modify the association between genetic variation in the FTO genotype and obesity. Am J Clin Nutr. 2009 Sep 2. [Epub ahead of print]
  • United States Department of Agriculture (USDA). Accessed online at http://www.health.gov/DIETARYGUIDELINES/dga2005/document/html/chapter6.htm
  • United States Department of Agriculture (USDA). Profiling Food Consumption in America, Chapter 2. Accessed online at http://www.usda.gov/factbook/chapter2.htm

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