by Craig Weatherby
Why are Americans increasingly overweight?
Three intriguing research reports were released this past week, all bearing on this critical question (click to skip to our summaries):
#1 - Can friends be fattening (or slimming)?
#2 - USDA study blames calorie cravings, not carb-cravings
#3 - Cane sugar and corn syrup exert similar effects on appetite
Prior evidence points to several possible factors:
• Calorie-filled fast foods.
• Sugary drinks.
• Starchy-fatty foods and snacks.
• Sedentary occupations and lack of exercise.
• Excessive intake of omega-6 fatty acids*.
*Mostly from standard, grain-fed meats and the vegetable oils most commonly used in home cooking and processed and prepared foods (corn, canola, soy, sunflower, safflower, and cottonseed.
But findings from the three new studies add more pieces to America’s obesity puzzle.
Study #1: Can friends be fattening (or slimming)?
You’ve probably heard about the new study suggesting that people’s weight is influenced heavily by how fat or thin their friends are.
In fact, it looks like body mass indices (weight-height ratios) of one’s friends matters more than the shape a spouse is in.
(Clearly, this rule didn't apply to 1930's movie comedy superstars Laurel and Hardy—pictured at upper left—or they weren't friends off-camera.)
Researchers from Harvard University and UCAL San Diego analyzed data from 12,067 adults who participated in the famed Framingham Heart Study and received regular medical exams during the 32-year-long investigation (Christakis NA, Fowler JH 2007).
They found that if a person you consider a friend becomes obese, your own chances of becoming obese go up 57 percent. And the effect is even stronger among groups of friends, with your chances of becoming obese increasing 171 percent if several in your circle become obese.
Conversely, if a friend or friends lose weight, your chances of becoming thinner go up.
It appears that people's influence on each other's obesity status wasn’t due to similarities in lifestyle and environment. And the striking impact of friends’ weight status seems independent of whether they live in the same region.
Be that as it may, we can’t affect our friends’ weight situation.
But we can address our own eating and exercise habits, so news out of Boston made us sit up and take notice.
If confirmed, the new findings may cast doubt on the notion, made famous by Dr. Robert Atkins of diet-book fame, that the rise and subsequent fall in blood sugar levels that follows consumption of easily digestible carbohydrates (sugars and starches) leads to a rapid cycle of carb cravings and consequent overload of calories borne by dietary carbs.
Study #2: USDA study blames calorie cravings, not carb-cravings
Low-carb, high-protein diets have generally shown a significant—albeit inconsistent—weight-loss edge over standard low-fat/low-calorie diets in head-to-head clinical trials.
However, low-carb/high-protein Atkins-style diets have not always conferred significant long-term weight control advantages when tested against standard low-fat/low-calorie diets, which tend to be high in carbohydrates.
But these comparative trials have tended to be as undiscriminating about the protein sources in the low-carb, high-protein diets as Dr. Atkins was.
When researchers test low-carb/high-protein diets that feature omega-3s more prominently, the outcomes favor low-carb/high-protein diets more strongly.
This is because dietary omega-3s push human metabolisms toward fat-burning and discourage storage of dietary calories as hard-to-lose body fat. For more information, see our prior articles on this subject:
- “Omega-3s Boost Weight Loss Benefits of Low-Cal Diets”
- “High-Protein Diets Called Most Helpful for Weight Control”
- “Wild Salmon Excels for Sports and Fitness”
- “Exercise + Omega-3s = Perfect Weight Loss Pair”
- “Eat Fish, Lose Weight, Feel Better”
Many critics place major blame for the growing obesity epidemic at the feet of a US food industry that packs processed foods with sugar and starch.
But the results from Boston suggest that the obesity challenge may be more complicated than a craving for carbohydrates in the form of sugary drinks and sweet or starchy snacks.
The recent report comes from scientists at the USDA Human Nutrition Research Center on Aging at Tufts University (Gilhooly CH et al 2007).
The study involved 32 overweight but otherwise healthy women, ranging from 20 to 42 years of age. The women were randomly assigned to two diets that differed in “glycemic load”: a measure of each diet’s proportion of easily digestible carbs.
The women completed questionnaires designed to assess the type of foods the participants craved, the frequency and strength of cravings, and how often cravings led to eating the desired food.
The one characteristic common to the foods the women craved was that all were high in calories. (Many of the craved foods contained carbohydrates, but also had substantial amounts of fat and some protein.)
The results suggest that food cravings are common in overweight women—a penetrating glimpse into the obvious, we suppose—with 91 percent of the participants reporting having them. And dieting only seemed to increase cravings slightly, with 94 percent reporting them after six months of dieting.
Unsurprisingly, the participants who lost a greater percentage of body weight were those who gave in to their cravings less frequently.
Study #3: Cane sugar and corn syrup exert similar effects on appetite
Many observers of the obesity and diabetes epidemics have blamed them in part on the rise in consumption of High-Fructose Corn Syrup (HFCS), which beverage makers began to use in place of costlier cane sugar in the late 1980’s.
Suspicions of corn syrup stem from the fact that obesity rates, which began to rise in the late '70s, really took off in the '80s, just when HFCS began to be widely used in processed foods.
Earlier this year, US and Finnish researchers reported finding no link between consumption of sweetened beverages and the risk of developing diabetes (See “Calories Seen Outweighing Sugar as Diabetes Risk”).
But obesity may be another matter, since numerous studies report associations between soft drink consumption and
|Are increased omega-6 intakes part of the obesity puzzle?|
The rise in obesity rates in the 1980’s also coincides with a sharp rise in the use of corn and soy throughout the food supply. As Michael Pollan explains in The Omnivore's Dilemma, corn and soy are used in most processed foods and are fed to almost every livestock animal.
This is one reason why Americans’ intake ratio of omega-3 to omega-6 fatty acids is so badly skewed toward omega-6 fatty acids, which tend to promote storage of calories as body fat.
(Corn has 46 times more omega-6s than omega-3s, while soy has seven times more omega-6 than omega-3: the ideal intake ratio is two-to-four parts omega-6s to one part omega-3s.)
In addition, while American’s average fat intake dropped from 41 percent of dietary calories in the mid 1960s to approximately 36 percent in 1984, omega-6 fatty acids have taken an increasing share of those fat-derived calories.
Even as intake of saturated and monounsaturated fatty acids fell from about 19 percent of calories in the early 1950s to 12-13 percent of calories in 1984, intake of polyunsaturated fatty acids—almost entirely fat-fueling omega-6s—more than doubled, from about 3 percent to 7.5 percent of dietary calories (Stephen AM, Wald NJ 1990).
- HFCS 55, which contains about 55 percent fructose and 45 percent glucose (“blood sugar”)
- HFCS 42, which contains about 42 percent fructose and 58 percent glucose (“blood sugar”)
This means that sucrose (cane sugar) actually has more fructose than much HFCS does, and contains only a bit less fructose than most HFCS does.
And it seems telling that obesity is also on the rapid rise in countries where sodas are still sweetened with cane sugar (sucrose): a fact that weakens the “HFCS-causes-obesity” hypothesis considerably.
The new study was led by Dr. Adam Drewnowski at the University of Washington in Seattle (Monsivais P, Perrigue MM, Drewnowski A 2007).
His team gave participants a beverage at mid-morning, then tracked their hunger, appetite and thirst for two hours, before giving them lunch.
The researchers compared the effects of different drinks on consumers’ appetites:
- Cola sweetened with sucrose
- Cola sweetened with HFCS 55
- Cola sweetened with HFCS 42
- Diet cola (aspartame-sweetened)
- Low-fat milk (one percent fat)
Lunch consisted of a wide variety of savory and sweet foods, served with water. Each participant went through separate tests for each type of beverage over the span of several weeks.
The results seem to absolve HFCS beverages of blame for stymied satiety signals and resulting excessive calorie consumption:
- Participants who drank the sugared colas or milk ate somewhat less at lunch, but only partially compensated for the calories they consumed in the beverage.
- Those who drank the sugared colas or milk consumed more total calories that day when both the beverage and lunch were taken into account.
- There were no differences in how the four caloric beverages (milk and sugared colas) affected appetite and food intake.
- Participants who drank the calorie-free diet cola ate about the same amount at lunch as when they had no beverage at all.
“There was no evidence that commercial cola beverages sweetened with either sucrose or HFCS have significantly different effects on hunger, satiety, or short-term energy intakes” (Monsivais P, Perrigue MM, Drewnowski A 2007).
The researchers found that the bond between fructose and glucose in the sucrose in the cane-sweetened colas tested broke readily, freeing the fructose to make as much metabolic mischief as the similar proportion of fructose in the colas sweetened with HFCS.
Accordingly, the authors suggest that the human body does not readily discriminate between beverages sweetened with sucrose and those sweetened with HFCS.
Of course, this study did not consider any long-term effects that HFCS might exert in the human body, which could have long term effects on appetite and fat storage: key questions that remain open.
The results of the new study are open to charges of bias, since it was funded in part by grants from the American Beverage Association and the Corn Refiners Association. However, it also received funding from the National Institutes of Health.
- Christakis NA, Fowler JH. The spread of obesity in a large social network over 32 years. N Engl J Med. 2007 Jul 26;357(4):370-9. Epub 2007 Jul 25.
- Gilhooly CH, Das SK, Golden JK, McCrory MA, Dallal GE, Saltzman E, Kramer FM, Roberts SB. Food cravings and energy regulation: the characteristics of craved foods and their relationship with eating behaviors and weight change during 6 months of dietary energy restriction. Int J Obes (Lond). 2007 Jun 26; [Epub ahead of print]
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