One of the enduring mysteries to me about the whole Dietary Guidelines issue is the extent to which my concerns regarding their effectiveness causes some folks to question my intelligence, knowledge, professionalism, and—I think—prescription drug use.
Take the graphic above, which appears to show a relationship in time between one event (the installation of a plastics factory) and another trend (rise in cancer rates). This does not demonstrate cause-and-effect, of course, but I think that most public health officials would be concerned enough about the clear inflection point and the following steep upward trend in disease to want to investigate the potential for a cause-effect relationship, or at least begin to ask some questions.
But when the graph looks like this, it’s a different story:
Every time I show someone the above relationship, I get remarks like, but what about physical activity levels? television? women in the work force? desk jobs? automobiles? anything, anything but the Guidelines!
Keeping in mind that the obesity graph above only shows the temporal relationship between when the Dietary Guidelines were implemented and when the rapid rise in obesity took place, I thought I would look at some of the other possible causes that are invoked in the name of avoiding the possibility that we’ve been wrong about public health nutrition for the past thirty years.
It’s not the Guidelines #1: For some reason, Americans got much lazier in the past 30 years than they have ever been before.
I will say right off the bat that we don’t have a lot of clear data about physical activity levels because we didn’t really start paying attention to it until Americans started getting fat. However, the 1983 Public Health Objectives for Americans offer some insight: “The American lifestyle is still relatively sedentary. The proportion of adults aged 18-65 regularly exercising has been estimated at just over 35% . . .” [From: Promoting Health/Preventing Disease. Public Health Service Implementation Plans for Attaining the Objectives for the Nation (Sep. – Oct., 1983), p. 155].
The most recent research—2010—on physical activity levels in America paints a much different picture:
This may not be the complete story, but there is little evidence to suggest that we have become radically more sedentary since 1980. And if we have, one would have to ask just why that would occur?
It’s not the Guidelines #2: Moms went to work, leaving the kids in front of TV sets!
Labor force participation rate of women by age of youngest child, March 1975-2007
Women began entering the workforce, even with small children at home, long before obesity rates began to climb.
It’s not the Guidelines #3: Blame television! Television came along and we all turned into couch potatoes.
Television was in over 85% of American homes in 1960, 20 years before obesity rates began to climb. (However, it is possible that MTV, which debuted in 1980 along with the Dietary Guidelines, is at the root of our obesity crisis—anything, anything but the Guidelines!)
It’s not the Guidelines #4: We used to work at physically demanding jobs!
With these wonderful graphs from the book The first measured century: an illustrated guide to trends in America, 1900-2000, by Theodore Caplow, Louis Hicks, Ben J. Wattenberg, I looked for a similar pattern to that of the obesity trend, a parallel trend that might be a primary factor in the rise in obesity in America. The dashed lines represent the beginning of the obesity measurements above (beginning in 1960), while the solid lines shows when the first Dietary Guidelines were released (in 1980). To find some sort of correlated trend, we would want to find a flat-ish sort of line between the dashed line and the solid one, followed by a steep incline after the solid line, showing a concurrent trend. Alternately, we might look for a curve similar to the obesity one, but shifted to the left, showing a trend that preceded the obesity one. I didn’t find either in the transition from manual labor to more sedentary jobs.
It’s not the Guidelines #5: In the past, we used to walk everywhere–or ride our scooters, or our ponies!
I grew up in the 70s. We rolled around in great big cars without our seat belts on. Not such a great idea, but cars were an integral part of Americans lives long before obesity rates took off.
It’s not the Guidelines #6: Some seismic shift in our eating habits made many of us gain weight at an alarming rate.
Wait a minute—this looks familiar. Hmmm. Dramatic rise in carbohydrate intake? Dramatic rise in obesity! Who’da thunk? And why did we start eating all those carbs? Not because we were sitting in front of the TV while our moms went to work (we were, but that’s not why). We started filling our plates with cereals and starches because the Dietary Guidelines told us to.
References:
Adabonyan I, Loustalot F, Kruger J, Carlson SA, Fulton JE. Prevalence of highly active adults–Behavioral Risk Factor Surveillance System, 2007. Prev Med. 2010 Aug;51(2):139-43.
Gross L, Li L, Ford ES, Liu S. Increased consumption of refined carbohydrates and the epidemic of type 2 diabetes in the United States: an ecologic assessment. American Journal of Clinical Nutrition, Vol. 79, No. 5, 774-779, May 2004
Public Health Reports (1974-) , Vol. 98, Supplement: Promoting Health/Preventing Disease. Public Health Service Implementation Plans for Attaining the Objectives for the Nation (Sep. – Oct., 1983), pp. 1-177
Eathropology 
Great analysis Adele. Thank you for doing the graph research for me. I now have a discussion and power point for the next discussion already for me to go.
Happy to help! Please do spread the word.
Adele, great post and great website!
I don’t agree that correlation must precede causation, but a good correlation allows one to focus more clearly on individual variables. The of seemingly increase in fat consumption and heart disease. As Gary Taubes pointed out in his book “Good Calories, Bad Calories”, increase in heart disease that supposedly correlated with fat consumption may have just been the result of better diagnosis thanks to the invention of the electrocardiograph machine. What also happened together with the perceived increase in fat consumption was also an increase in carbohydrate consumption. Thus, there was a seemingly ‘good’ correlation between fat consumption and heart disease but there is a good chance that it was better diagnosis of heart disease what made that correlation look good in the first place. Heart disease may have always been there but we didn’t know how to diagnose it early enough.
In the case explained in this post, these and other correlations invariably lead to the alternate hypothesis that the Dietary Guidelines have had a detrimental impact on the health of Americans (the null hypothesis being that the guidelines have nothing to do with the deterioration of our health). The prediction of the alternate hypothesis (which helps in the design of direct, or at least more focused studies) would be that if we do something opposite to what the guidelines recommend, the outcome would also be the opposite. The evidence thus far suggests that. In fact, the evidence is so abundant now that it is not a stretch to say that it is in fact the implementation of the dietary guidelines that has negatively impacted the health of Americans. The hypothesis that it is the dietary guidelines that have negatively impacted our health cannot be easily rejected. Perhaps we are just too shy to actually say it categorically but what the science is telling us is precisely that: 1) implementing the dietary guidelines had a detrimental impact in our health and 2) following them will not likely improve it over time.
Gabe, So nicely stated! I ran out steam before getting to how we would test the hypothesis raised by the observation that the Dietary Guidelines may have had a negative, rather than positive impact on the health of Americans. The Gardner et al study in 2007 and the Shai et al study in 2010 are reasonable attempts to address this hypothesis in an experimental setting.
But what I’ve found happens in response to studies such as these is not “Oh geez, we’d better dig a little deeper here,” but “Hey, all those low-carb folks reduced their calories spontaneously! See, it’s just calories in calories out.” Or, (I like this one a lot), at the end of the study–after some pretty remarkable weight loss–as the low-carb arm starts “adding carbs” back into their diet AS DIRECTED BY THE STUDY, they gain weight to the point that their weight loss is approximately equivalent to those in the other arms of the study. Then, those commenting on the study (the researchers themselves and others) can say, “Well, reducing carbs didn’t really make that much of a difference anyway. See, it’s just calories in, calories out.” And of course any improvement in health risk factors can be explained by the weight loss, which, of course was just a matter of (all together now, in three-part harmony)”calories in, calories out.”
I don’t get too excited about the inherent biases; we know they are there. But lousy logic is just lousy logic.
Oh, trust me, I know what you mean. However, there is also plenty of evidence that quite simply trumps the calorie-is a calorie-is a calorie concept, as well as the ‘the composition of the calories in the diet doesn’t matter’ type of thinking. That research is not new… Yudkin already showed that in the 60’s, some 40 years after Ancel Keys did his semi-starvation study. Other, more recent studies, have done the same. When we put all that evidence together, well it is pretty convincing that it is not just the amount of calories per se, but the actual metabolic effect of reducing carbohydrate what plays a role, sometimes not even decreasing caloric intake that much (for example in studies where weight loss is not the measured outcome).
What the nay-sayers don’t want to understand is that nobody is saying that reducing carbohydrates doesn’t reduce calories, in fact it does, but it is a smarter way of reducing calories without starving tissues from what they really need. Since reduction in carbohydrates usually comes with an increase in protein and fat, increased protein intake has been shown several times that increases both thermogenesis and satiety; we ‘burn’ a bit more while not feeling hungry all the time, which in turn translates into not eating so frequently, which in turn translates into decreased food intake… in other words, yes, calories are reduced, but 1)it happens voluntarily because satiety is increased and 2) it happens without jeopardizing energy supplies for tissues because they’re getting what they really need (protein and fat), not what they don’t need (carbohydrate).
Jeff Volek and Steven Phinney, in their book “The Art and Science of Low Carbohydrate Living” explore (and pretty much debunk) the myths (or ‘concerns’ as they put it) of low-carbohydrate diets, from the ‘it’s all water loss…” to “your bones will break and your kidneys will fail…” They also devote an entire chapter to explain the energetics of low carbohydrate diets, all based on science. You would think that it would be enough already and that we should move on to accept the facts but no… is like being in the dark ages all over again!
It’s just amazing to me that I still hear the same question over and over again… ‘what are the long-term effects of low-carbohydrate diets’ but nobody wants to admit the long-term, detrimental effects that the low-fat, essential nutrient unbalanced diet recommended in the dietary guidelines. Isn’t 40 years long enough to recognize its dismal failure? While even short-term (1 year or less) already show the detrimental effects of the diet recommended by the guidelines, none has shown detrimental effects of a well designed low-carbohydrate study (a true low-carbohydrate diet study, not something that says that in the title but it is not, in fact, a low but ‘lower’ carbohydrate diet attempt). Even the mediocre studies show benefit. That should say something, shouldn’t it?
Thank you for the references!
The public health responses I constantly am trying to counter are that the rapid rise in obesity/diabetes happened because 1) people don’t follow the recommendations they are given or 2) we live in an “obesogenic” environment that has nothing to do with the Guidelines (!?). In public health, the most common response I get to “well, lowering carbs works . . . ” is a knee-jerk Atkins-diet-kills-you gasp. We have a long way to go. I wish it would be as easy as just accumulating the science and getting the facts out there–I’m afraid there’s much more to it than that.
You can’t have causation without first having correlation, and there is clearly a correlation between the publication of the Dietary Guidelines and rates of obesity.
At the very least, you’d think that people would look at it and go, “What the hell?”
You would think. This is why it is a mystery to me. As students and scientists we are supposed to question–to “think critically”–except about this. The more I explore the cultural roots of the Guidelines and our national food policy in general, the more I run into a weird cooperative tension between the ideology that frames a plant-based diet as more virtuous (for the environment, the world’s hungry, the poor animals, etc) and corporate agribusiness that, indeed, would love for us to all adopt that mindset. Jonathan Safran Foer-novelist turned veg*n activist–pushes his agenda by summoning the expertise of “the nation’s premier group of food and nutrition professionals” the American Dietetic Association (now the Academy of Nutrition and Dietetics), ignoring the fact that they are sponsored by the National Dairy Council and best buddies with the USDA, two groups that he goes on to criticize as warping the content of the nutrition information that Americans receive (from, um, dietitians trained by the ADA/AND), along with “the distorting influence of the meat industry.” He seems like a smart guy, so how does he make his brain turn off like that? The USDA and the National Dairy Council would be thrilled if we all became vegetarians (at least lacto-ovo-vegetarians); there is a lot more money to be made from skim milk, soybean oil, and granola bars than from a pork chop any day.