Did the US Dietary Guidelines Cause the Obesity Epidemic?

A popular argument holds that the US Dietary Guidelines caused our obesity epidemic by advising Americans to reduce fat intake.  Does the evidence support this idea, or is it simply a fantasy?


Low-fat diets have fallen out of style and are now a favorite punching bag in some corners of the popular media, the Internet, and the scientific literature.  And there are reasons for this.  As typically implemented, low-fat diets have largely failed to live up to their promise of reducing the risk of obesity, cardiovascular disease, and diabetes.  Randomized controlled trials over the last two decades have increasingly supported the position that higher-protein, lower-carbohydrate, and sometimes higher-fat diets promote greater weight loss than low-fat diets over the short- to medium- term.

The truth is that this is a significant medical reversal.  Researchers and public health authorities accepted a hypothesis– and dispensed advice based on it– to later learn that the hypothesis was not as well supported as they had thought.  This is fair to point out.

Yet this idea often gets pushed a step further: by shifting our diets away from fat and toward carbohydrate beginning in 1980, the US Dietary Guidelines actually contributed to the obesity epidemic.  This idea has been promoted in several popular books, and most recently, in an editorial published in the Journal of the American Medical Association (1).  Here is the relevant quote:

As a result of [US dietary guidelines], dietary fat decreased to near the recommended limit of 30% total energy. But contrary to prediction, total calorie intake increased substantially, the prevalence of obesity tripled, the incidence of type 2 diabetes increased many-fold, and the decades-long decrease in cardiovascular disease plateaued and may reverse, despite greater use of preventive drugs and surgical procedures. However, other changes in diet (such as meals away from home) and lifestyle (such as physical activity level) may have influenced these trends.

Recent research suggests that the focus on dietary fat reduction has directly contributed to this growing burden of chronic disease.

As usual, when someone makes a factual statement, they are stating a hypothesis.  Whether or not the hypothesis is correct depends on whether its key predictions are supported by compelling evidence.  So let’s go through some key predictions of this hypothesis and see if the evidence supports them.

Prediction 1: There should be a correlation between the publication of the Dietary Guidelines and the obesity epidemic

The US government has been publishing dietary information for at least 120 years, and the 1980 version wasn’t the first to recommend limiting the intake of fatty foods (2).  Still, it could be argued that the 1980 version was more strongly worded and more influential of public eating habits.

Americans have been growing fatter for over a century (3), but the trend has accelerated over the past 3-4 decades, and we call this acceleration the “obesity epidemic”.  This epidemic was first clearly detected by the 1988-1994 NHANES survey.  The previous survey was conducted between 1976 and 1980, so we can say that it began sometime between 1980 and 1988 (4).

Roughly speaking, it is true that there’s an association between the publication of the 1980 Guidelines and the obesity epidemic.  Yet by itself, this is very weak evidence, due to the large number of other things that also changed over that time period.  For the hypothesis to be credible, it will need more support.

Prediction 2: Americans should have reduced our fat intake in response to the Guidelines

If the Dietary Guidelines caused us to gain weight by putting us on a low-fat diet, there should be evidence that we actually began eating less fat in response to the Guidelines.  If not, the hypothesis cannot be correct.

Two independent lines of evidence suggest that our absolute fat intake did not decline after the publication of the Guidelines (5, 6).  Proponents of the hypothesis invariably cite the fact that the percentage of fat in the US diet declined, which is true (although the change was rather small).  The reason the percentage changed is not because our fat intake decreased, but because our carbohydrate intake increased, along with our total calorie intake.  Does this count as a low-fat diet?

As an analogy, imagine a man named Jim who has obesity.  Jim wants to lose weight, so he decides to eat a low-carbohydrate diet.  Rather than reducing his intake of carbohydrate, Jim adds fat to all his meals so that the percentage of carbohydrate in his diet decreases.  Jim’s calorie intake increases from 3,000 to 4,000 Calories per day, and his absolute carbohydrate intake remains the same.  Yet the percentage of carbohydrate in his diet decreases from 45% to 34%.  Is Jim on a low-carbohydrate diet, and should we expect him to lose weight?

Of course not.  Jim isn’t eating a low-carbohydrate diet, and neither have Americans been eating a low-fat diet.

3. Low-fat diets should cause weight gain

For this hypothesis to be correct, low-fat diets have to cause weight gain.  While low-fat diets as typically implemented may not be a very effective weight management tool, decades of research shows that they cause weight loss, not weight gain.  This is true even when we only consider studies that didn’t involve deliberate calorie restriction (7, 8).

The fact that low-fat diets cause less weight loss than low-carbohydrate diets over the short- to medium-term doesn’t mean low-fat diets cause weight gain.  Both diets are more slimming than eating as much as you want of everything.

4. People who followed the Guidelines should have gained more weight than people who didn’t

If the Guidelines caused the obesity epidemic, then the people who actually followed the advice should have gained more weight than the people who didn’t.  Yet the evidence shows precisely the opposite (9).  Here’s the money quote:

Poor compliance with the Guidelines, rather than the guidelines themselves, is likely responsible for the weight gain observed in the American population. Adoption of an eating pattern consistent with the Dietary Guidelines should facilitate population weight control if sustained long term.

5. Other countries with dissimilar dietary guidelines should not have a similar obesity problem

I’m not going to do an in-depth analysis of how national dietary guidelines relate to changes in weight, but I’ll simply point out that nearly all affluent nations have been gaining weight rapidly in recent years, regardless of dietary advice or lack thereof (10).  The US is only unique in the sense that we’re on the leading edge of economic, dietary, lifestyle, weight, and health changes that are affecting the entire affluent world.

The verdict

Although the low-fat diet doesn’t appear to be a silver bullet for our national weight problem, the hypothesis that US Dietary Guidelines caused the obesity epidemic by reducing our national fat intake has more holes in it than Swiss cheese on baguette.

5 Responses to Did the US Dietary Guidelines Cause the Obesity Epidemic?

  1. I’d say that more than anything it’s a facile argument.

    Weight gain is multifactorial. Adding the Guidelines as a factor in a least squares equation (0=before, 1=after) predicting % obesity would be easy enough. But factors such as calories consumed by macronutrient type, or % of meals eaten in fast food restaurants, or GB of personal bandwidth available, would probably be more significant.

    Doing something like this would at least put a sense of scale on the importance of the argument. On the face of it it seems unimportant, because you can’t go back in time and change anything.

    If I recall correctly, Yudkin once graphed UK television licenses granted vs obesity and found a strong correlation…

  2. My understanding is that fat is stored unlike carbohydrates which are broken down much quicker. Would you say that could be a reason increased carbohydrate intake did not correlate with a decrease in total caloric consumption, due to its inability to satiate.

    I’m also basing this thought off of an article on leptin inhibition [https://authoritynutrition.com/leptin-101/] which lead me to your site.

    Great stuff. Your reply would be greatly appreciated and well received 🙂

  3. Reading and rereading Keys and Yudkin’s ca 1960 diet books, I get a sense that what was missing in the Guidelines is the definition of “serving”.

    Both Keys and Yudkin are very clear on what it is, and they back it with sample menus. Because they both subscribe to CICO, weight loss diets for a typical woman readers of their books are on the order of 1200 calories per day (though Keys seems to emphasize normal diets rather than weight loss). The difference between the two of them is seen mostly in Keys replacement of hard fats with cooking oils, and in Yudkin’s reduction in high glycemic carbs (both sugars and starches). But for a 1200 calorie diet it is implicit that the food portions in a serving are small, on the order of 70-100 calories.

    Yudkin provides only one sample diet (TSB, p160), and he provides 5 pages of tables to construct others. No recipes and no references…the readers are left to puzzle that out for themselves. It is interesting to see how Yudkin’s 15 CU weight loss diet is built. 3 meals, 3 snacks. Breakfast consists of bacon, eggs, buttered bread and half a grapefruit. First snack tea or coffee. Lunch stewed beef, brussels sprouts, buttered starch-reduced rolls and fruit salad with cream. Second snack tea and a sweet biscuit. Dinner grilled fish, spinach, buttered potato and sharch reduced rolls, cheese. Third snack cocoa. I estimate this to be about 1200 calories. Oddly, Yudkin includes no milk, though there could be milk or cream with the coffee/tea he shows at every meal, and with the cocoa.

    Keys provides 32 pages of daily eating plans, followed by 82 pages of recipes (thank you Margaret Keys for both), followed by 14 pages of calorie and nutrient tables, followed by 80 references (12 on wine alone). Picking a typical day (“Winter Tuesday, EWSW p 181), there are 3 meals and 1 snack. For the 1800 calorie version (there is also a 2200 calorie version alongside), breakfast consists of 1/2 a serving of oatmeal, 2 oz skim milk, 1t sugar (440 calories, 13 g protein, 7 g fat). Lunch consists of macaroni and tuna casserole (1/2 recipe), stuffed baked tomatoes, a lettuce sandwich, a cup of skim milk, and 1/2 a recipe of Danish dessert(a pudding made with fruit juice, corn flour and sugar) (720 calories, 34g protein, 10g fat). Afternoon snack of tea and buttered bread (50 calories). Dinner Fegato Veneziana (a sautee of onion, calves liver and white wine), boiled potato, green salad with french dressing and Apple Betty (680 calories, 27g protein, 23g fat). Total for the day 1890 calories, 72g protein, 42g fat.

    As you read the two side by side, it is obvious that Yudkin is more colloquial. Yudkin’s CU methodology is very flexible, but leaves everything to the reader to implement. Keys is very details-oriented, and backs it up with numbers. Neither minces details about how MUCH you should eat. At the very end of his book Yudkin says

    “There are still some people about who imagine all they need in order to slim is to get advice. They do not seem to get around to the idea that the advice also has to be followed. They might just as well write up a slimming diet, and put it under their pillow.”

  4. I think most people above a certain age will remember when the great switch away from fat came as it was so sudden and overwhelming.

    However what drove the switch directly wasn’t the government guidelines but the low fat advertising that (I assume) started as a consequence of the guidelines.

    A recent documentary on the BBC included an interview with a woman who’d worked in the food processing industry since that time who said they removed the fat as per the guidelines so they could get more sales but found people hated the taste – so they replaced the fat with sugar.

    (which was against the guidelines)

    So although it might be wrong to say the guidelines caused the obesity epidemic (especially as they said less sugar also) it seems the guidelines might have been the catalyst for the chain of events that led to the obesity epidemic.

    If switching fat to sugar in processed food was the trigger in some way then given your other points maybe it’s not calories or type of calories in sugar vs fat but something else in the fat that wasn’t in the sugar – for example does sugar have less iodine thereby maybe leading to a slower metabolism?

    (I mention this as I recently started topping up iodine as an experiment and as well as being more alert and productive i appear to be losing weight without dieting.)

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