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Genes and Diet Choice

Why genetic predisposition is not the answer

A friend alerted me to a study showing that some women lose weight on a low-fat diet, while others do better on a low-carb diet. (Genes Point to Best Diet, WSJ 3/4/10) It’s in their genes, according to the study. A simple DNA analysis, costing $149, determines whether you are a low-fat person or a low-carb person. My friend thought it would be money well spent. I wasn’t so sure. It didn’t sound like a realistic long-term solution.

Let’s discuss it. We’ll begin with the study, which was presented by Stanford University researchers at the American Heart Association’s annual epidemiology and prevention conference in San Francisco; it hasn't cleared peer review for publication, but was approved for presentation at the conference.

DNA Determines Diet

A study of 138 overweight women found that “those with a genetic predisposition to benefit from a low-carbohydrate diet lost 2 ˝ times as much weight as those on the same diet without the predisposition,” Ron Winslow wrote in The Wall Street Journal. “Similarly, women with a genetic makeup that favored a low-fat diet lost substantially more weight than women who curbed fat calories without low-fat genes.” The women were on the diets for a year.

Sounds great. Knowing your diet genotype would give you a big leg up on losing unwanted pounds—or so it seems.

An earlier study found that a substantial proportion of white women are genetically suited for low-carbs or low-fat, 45% and 39%, respectively. Confirmation by a larger and more inclusive study will be required, according to the Stanford researchers.

“The results suggest even strict adherence to a diet won’t matter if people’s diets are out of synch with their genetics,” said Dr.Christopher Gardner, co-author of the new study.

We should remember, however, that larger studies have found that calories matter most, not the relative proportion of carbs, fat, or protein; see Calories Count: http://www.cbass.com/CaloriesMatter.htm. Macro-nutrient composition didn’t seem to matter in those studies.

The Journal article referenced this earlier finding: “In the past decade, about a dozen studies pitting low-fat vs. low-carb diets have been published in major medical journals,” Winslow writes. “For the most part, no winner has emerged, and none of the diets resulted, on average, in weight loss exceeding 10 pounds in a year.”

The Stanford researchers suggest that their study may explain why diets don’t work very well “on average.” Matching diet and genes might change that, they argue. “[Our study] makes the whole topic relevant again,” said Professor Gardner.

Gardner did, however, acknowledge that matching diet and genes doesn’t insure success. “If low-carb people make a diet out of low-carb cupcakes,” Gardner cautioned, “they’re unlikely to see the results they want on a scale.” In other words, calories still matter.

While it’s true that the women who ate according to their genotype lost substantially more than those who didn’t, they still didn’t have much to show for their year of dieting—a loss of 14.1 pounds for those with the low-fat genes and 12.3 pounds for the low-carb women. 

Losing a conservative half pound a week would add up to a little over 25 pounds in a year. Something is still amiss. It seems to me that these women have yet to find the formula for losing weight and keeping it off.

The women—low-fat and low-carb—would’ve done better with a balanced diet of satisfying, whole foods (ample carbs protein and fat), and regular exercise. They should take care to avoid hunger and feeling deprived. The key to permanent body fat control is eating satisfaction. Few people will stick to an eating plan that leaves them feeling unsatisfied. (See the discussion of human food instincts in my earlier article Calories Matter: http://www.cbass.com/CaloriesMatter.htm.)  

As luck would have it, we have another new study that looked at the effects of low-carb (high fat) and low-fat (high carb) diets on mood.

The Mood Factor

The Johns Hopkins Medical Letter (March 2010) summarized the findings as follows: “The mood-lifting effects of weight loss may depend, in part, on the type of diet people choose. In a recent year-long study, 106 obese [and overweight] people were randomly assigned to a very-low-carbohydrate, high-fat diet (such as Atkins) or a very-low-fat, high-carbohydrate diet. They found that although both groups lost the same amount of weight (about 30 pounds), only the low-fat, high-carbohydrate group reported consistent improvement in mood.” (Emphasis mine)

Let’s delve the details, which are reported in the Archives of Internal Medicine (November 9, 2009).

Importantly, the researchers (from Australia) assessed the long-term effects of the two diets on psychological function—how the people felt while on the diets. “Weight loss as a result of dieting in obese individuals has been shown to reliably improve psychological state, including mood,” the researchers wrote in introducing the study. They noted, however, that the research is incomplete: no study had documented the effects “beyond a few weeks.”  They extended the study of the “effects…on mood” for a full year. 

As we’ll see, the short- and long-term effects proved to be different.

Calorie count was the same in both diets, 1433 for women and 1672 for men. The prescribed low-carb diet (LC) contained 4% carbs, 35% protein, and 61% fat; carbs were restricted to 20 grams a day for the first 8 weeks, with the option to increase intake to 40 grams thereafter. The low-fat diet (LF) contained 46% carbs, 24% protein, and 30% fat. Participants met individually with qualified dieticians every two weeks for the first 8 weeks, and monthly after that. The 30 pound loss in both groups suggests that compliance was good.

Participants were tested for changes in mood at the beginning of the study and again at weeks 8, 24, 40, and 52. Three questionnaires were used assessing different aspects of mood state, including hostility, confusion, depression, and anxiety.

The low-fat (high carb) diet was found to have favorable effects on feelings and emotions throughout the year-long study.

The researchers reported “rapid improvements in mood during the first 8 weeks with both diets.” Over the long-term, however, “many of the benefits regressed in the low-carb diet group…Participants on the low-fat diet [high carb] achieved better outcomes.”

Why the difference?  

The Johns Hopkins Medical Letter offered one possible explanation: “Carbohydrates help synthesize the feel-good neurotransmitter serotonin, so consuming less may lead to dampened spirits.”  

Let’s look to the full report once again.

While the researchers have no “complete explanation,” they offer “several plausible reasons” for the different impact on mood.

The first is a social effect: “The LC diet being so far removed from normal dietary habits may have created a significant challenge for participants, leading to the possibility of food preoccupation, social eating impairment, [depression, and anxiety]. Although, in the short term, participant may have been able to meet the challenges…over the long term, it may have increased participant isolation, leading to the negative impact on mood state.”

The second plausible reason is convenience. “The possibility that the prescriptive [rule bound] nature of the dietary regimens had a negative impact on [feelings and emotions] should also be considered,” the Aussie researchers wrote. People find it time-consuming and inconvenient to count grams of carbohydrate, protein, and fat. That’s also a factor in low-fat diets, but perhaps to a lesser extent. The “highly prescriptive” nature of the LC diet may have alienated some participants, the researcher surmised.

The final explanation is physiological; it’s the most objective and one chosen by The Johns Hopkins Medical Letter: “Mood among long-term consumers of LC diets may also be negatively affected by changes in serotogenic expression…,” the report states. “While a high-carbohydrate intake can increase serotonin synthesis, fat and protein intake reduces serotonin concentrations in the brain.”

As The Johns Hopkins Letter indicated, serotonin is a “feel-good neurotransmitter.” Neurotransmitters are essentially chemical traffic cops in the brain that balance psychological state. Psychiatrists use drugs which focus on the neurotransmitters to keep their patients feeling and acting normally.

“There is an abundance of evidence demonstrating a link between serotogenic functions of the brain and aspects of psychological functioning, particularly depression and anxiety,” the report explains.  

That may seem complicated, but it simply means that people on low-carb, high-fat diets are often lethargic and anxious; Oprah famously said she would “kill for an apple” after a short time on a low-carb diet. Many low-carb dieters simply don’t feel well.

That also happens when we cut calories too much; blood sugar drops and we tend to drag through the day. Simply put, low-calorie dieting (low-carb or low-fat) is the pits, it’s unpleasant. Neither diet is likely to work very long; they’re not good vehicles for keeping weight off.

Genes Not the Answer

Genes may point the way, but they’re still not the answer. 

All of the explanations listed above may combine, in one way or another, to dampen the spirits of low-carb dieters. Be that as it may, some people probably feel better than others on a low-carb diet. The same goes for the traditional low-fat diet. Genes may indeed play a role in diet preference. 

That doesn’t change the fact that low-calorie diets, whether low-carb or low-fat, work poorly, especially over the long-term. That’s why up to 90% of people gain back all the weight they manage to lose by dieting—and often more.

I seriously doubt that genetic predisposition is the answer for overweight people. Diets simply don’t work, whether or not they are in accord with genetic preference.

We need an eating style that moderates calories without leaving us feeling hungry and deprived. A balanced diet of whole foods—combined with exercise—does precisely that. You almost never leave the table feeling unsatisfied. You feel full and and satisfied--and ready to go on with your day. Your body fat goes down slowly but surely—and stays down. The only thing you’ll want to count is the pounds of fat you lose. 

It has worked for me for over three decades. I believe it will work for most people. Try it, you’ll like it.

Here’s some more details on my eating style/philosophy: http://www.cbass.com/PHILOSOP.HTM

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