Tuesday, March 24, 2015

Study Links Rise in US Obesity Rates to Adherence to US Dietary Recommendations, But Don't Confuse Correlation With Causation in Your Vendetta Against Carbohydrates

Is the USDA to blame for this?
If you are a regular, here at the SuppVersity, you will be aware that I am not exactly a fan of the USDA's dietary recommendation. With good reason as the results of a recent statistical review in the peer-reviewed scientific journal Nutrition appears to suggest.

In the corresponding paper, the authors present the first comprehensive analysis of that data, documenting how macronutrient consumption patterns and the weight and body mass index in the U.S. adult population evolved since the 1960s. What they found is... well, not exactly in support of what the USDA did over the past decades.
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In 1961, spurred by emerging medical and epidemiological research, the AHA issued dietary recommendations to “reduce the intake of total fat, saturated fat, and cholesterol” (Kritchevsky. 1998). In 1977, the U.S. Senate Select Committee on Nutrition and Human Needs issued Dietary Goals for the United States (“Dietary Goals”), which recommended that fat consumption be reduced to 30% of energy intake, and that carbohydrate consumption be increased to account for 55-60% of energy intake (SCNH. 1977).

In short: The feds told the US citizens to eat more carbohydrates and less fat and the public obeyed. According to the official USDA data (at least most of it is from the NHANES studies) the scientists analyzed, the fat consumption by U.S. adults has decreased from 45% to 34% between 1965 and 2011. At the same time, the intake of carbohydrate has increased from 39% to 51%.
Figure 1: The recommended changes in dietary habits went hand in hand with the increase in BMI (Cohen. 2015),
A change in dietary habits of which statistics cannot tell us that it fueled the ever-increasing number of overweight and obese adults in the USA, but one that unquestionably correlates with the rise in obesity. An observation the scientists use to conclude:
Figure 1b: What forget is that their data also shows that the absolute amount of fat US citizens consumed (in g | see Figure 1b) did not decrease. So, essentially the claim that the US citizens followed the guidelines is questionable.
"In the first comprehensive statistical analysis using all available NHANES surveys, this paper demonstrates that general adherence to government dietary recommendations to decrease fat share of total dietary intake has been accompanied by a rapid increase in obesity rates. 
The results in this paper compel a full analysis of the potential causal relationship between Americans seeming adherence to the government’s nutrition recommendations and obesity" (Cohen. 2015).
Now as convincing as this may seem to the laymen, the scientists are careful enough to use the important wort "potential" in the conclusion of their analysis of the data. A small word with far-reaching implications. Firstly, the absolute data in Figure 1b shows that there is no decrease in absolute fat consumption. A fact that leads me to a second, more important point. Th relative reduction in fat intake went hand in hand with other changes in the US diet. Mostly, an increase in total energy intake which came mostly from carbohydrates (see Figure 1b). But there is more: Examples?
Figure 2: The changes meal and snack food energy intake in youths (left | Jahns. 2001) and, more importantly, the correlation between body weight and energy intake (right | Swinburn. 2009) make the reasoning that the dietary recommendations and a shift from fat to carbohydrates alone had triggered the obesity epidemic look stupid.
Well, what about the increased prevalence of snacking? Both, high carbohydrate and high fat (mostly high fat + high carbohydrate) foods that contributes to increased obesity rates specifically in US kids and adolescents (Jahns. 2001). The increase in sweetened beverages (+54% in all age groups, 67% in the 19-39 year olds) from the 70s to the 90s (Nielsen. 2004). And, most importantly, the previously hinted at increase in portion sizes (Nielsen. 2003) and total energy intake, of which Swinborn et al. argue in their 2009 article in the Journal of the American Society of Nutrition quite convincingly that it "is more than sufficient to explain the US epidemic of obesity" (Swinburn. 2009).
Study confirms: The Standard American Diet (SAD) yields 'optimal' results when the goal is to fatten up human beings | more
Again, correlation and causation are two different pairs of shoes. If the Americans ate the same amount of highly processed junk with higher fat and lower carbohydrate content, they'd be just as fat today. In fact, overfeeding studies previously discussed at the SuppVersity indicate that optimal fat gain - even in humans - happens in a high fat (albeit not low carbohydrate) scenario (read more)

In view of the inability or unwillingness of those who have been defending their own useless recommendations for decades to finally be straight with people and tell them that the mere recommendation to eat more carbohydrates and less fat is bullocks, you could still argue that the USDA with its sacred "low fat" mantra did - if not promote the obesity epidemic - at miss the chance to keep the ever increasing obesity rates at bay | Comment on Facebook!
  • Cohen, Evan, et al. "Statistical review of US macronutrient consumption data, 1965–2011 Americans have been following dietary guidelines, coincident with the rise in obesity." Nutrition (2015).
  • Jahns, Lisa, Anna Maria Siega-Riz, and Barry M. Popkin. "The increasing prevalence of snacking among US children from 1977 to 1996." The Journal of pediatrics 138.4 (2001): 493-498.
  • Kritchevsky, David. "History of recommendations to the public about dietary fat." The Journal of nutrition 128.2 (1998): 449S-452S.
  • Nielsen, Samara Joy, and Barry M. Popkin. "Patterns and trends in food portion sizes, 1977-1998." Jama 289.4 (2003): 450-453.
  • Nielsen, Samara Joy, and Barry M. Popkin. "Changes in beverage intake between 1977 and 2001." American journal of preventive medicine 27.3 (2004): 205-210.
  • Select Committee on Nutrition and Human Needs of the United States Senate. Dietary goals for the United States [Internet]. 2nd ed. Washington: U.S. Government Printing Office; 1977.
  • Swinburn, Boyd, Gary Sacks, and Eric Ravussin. "Increased food energy supply is more than sufficient to explain the US epidemic of obesity." The American journal of clinical nutrition 90.6 (2009): 1453-1456.