Persistent Magical Thinking About Fruits and Veggies
What’s the #1 way Americans are fighting obesity? You guessed it. We’re eating less and moving more. What’s #2? We’re eating more fruits and veggies and salads. Sadly though, these efforts aren’t paying off. Despite putting those great ideas into action, the prevalence of obesity keeps rising. It’s now at an all time high of 40%.
We just might be the victims of magical thinking. And some of the most magical thinking fuels the ongoing campaign to get us all to eat more fruits and veggies.
Fruits and Veggies Are Definitely Good for Us
Make no mistake. Fruits and vegetables are good for us. Eating more of them and less of sugary, calorie dense foods would do us a world of good. And if indeed, our diets had less of the junky stuff and more of the marvelous fruits and vegetables, we might weigh a little less.
But the problem comes with figuring out how to get there.
Eat More Fruits and Vegetables!
Marketing campaigns need a simple message. And the simple message on this subject has boiled down to eat more fruits and veggies. The theory is that people will just naturally eat less of the other stuff.
However, a different reaction is to add a salad alongside that 800-calorie burger you were going to have anyway. Mission accomplished. Is that what real people in the real world would do? Or would they eat fewer burgers and shed a few pounds?
Pesky Data
To answer these questions we have a bunch of studies and a pair of systematic reviews. In 2014, Kathryn Kaiser and colleagues published a systematic review and meta-analysis. Based on the evidence at hand, they concluded that simply urging people to eat more fruits and veggies will not lead to weight loss or obesity prevention. You’ve got to do something to discourage consumption of all that other stuff if you want to have an effect.
Also in 2014, Oliver Mytton and colleagues published another systematic review and meta-analysis. They reached the opposite conclusion. Promoting fruit and vegetable consumption – even in the absence of advice to eat less of the other stuff – “may have a role in weight maintenance or loss,” they said.
But it turns out that the Mytton study had some significant statistical errors in it. Kaiser et al identified those errors in 2015. Finally, three years later, Mytton et al addressed those errors by publishing a lengthy erratum.
They concede that adjustments for these errors weaken their results, and even may render them statistically insignificant. But they’re sticking with their original conclusions anyway. Their wording was cautious, they say. True believers hold fast, despite pesky data.
Stubbornness Is Not a Virtue
Fighting obesity with strategies for which no effect is observable is getting us nowhere. We need more curiosity and better research to find strategies that will really work.
Click here for Kaiser’s study and here for Mytton’s study. For Mytton’s corrections, click here.
Burger and Salad, photograph © Cambridge Brewing Co. / flickr
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July 15, 2018
July 16, 2018 at 6:27 am, Leah Whigham said:
Ted, thanks for highlighting this important topic. In fact, we tested this hypothesis directly several years ago (I mention it here because the study was not included in the Kaiser review):
60 volunteers with obesity were recruited for a weight loss study. They were randomized to a typical calorie-restricted diet (500 kcal per day reduction) or a focus on consuming 8 servings of vegetables per day and 2–3 fruits per day. Food was provided for the first 4 months (along with education to follow the diet), then everyone was followed for a total of 18 months.
Initial analysis by study group randomization indicated both groups lost weight, but the calorie-reduced group kept it off better (https://www.ncbi.nlm.nih.gov/pubmed/19234056).
However, because increased fruit and vegetable intake is so often promoted for weight loss, there was no way to ensure the calorie reduction group would not also increase F&V intake. Therefore, in a follow-up analysis (https://www.nature.com/articles/nutd201222) we used a biomarker for total F&V intake (serum carotenoids) and found that, indeed, both groups increased F&V intake over the course of the study and that “Changes in weight, fat and % fat correlated negatively with serum carotenoid concentrations.” So our conclusions were that:
“… increased V&F consumption is an appropriate strategy for weight loss. However, in light of the fact that the (calorie) Reduction group lost more weight, the consumption of increased V&F for the purpose of weight loss should happen within the context of reducing total caloric intake.”
For this reason, in our translational work at the Institute for Healthy Living http://www.pdnihl.org we make sure to communicate this – albeit slightly less simple message – to eat more F&V but to do so in the context of reduced caloric consumption if weight loss is the goal.
Thanks for all of your great work communicating about the important nuances related to obesity!
–Leah Whigham, Executive Director of the Paso del Norte Institute for Healthy Living, and Associate Professor at the University of Texas at El Paso
July 16, 2018 at 8:28 am, Ted said:
Outstanding insight, Leah. Thanks!
July 17, 2018 at 2:54 am, James Jennings said:
This sounds like the advice to drink 8 glasses of water. The idea was that people would drink fewer sugary drinks because they were properly hydrated with water. But increasing water didn’t decrease liquid calories.
Fruits and veggies is based on the assumption that people will eat more of them and decrease consumption of more calories of other foods.
These would be implied effects. Not even correlation.
July 23, 2018 at 8:15 pm, Paul Ernsberger said:
As health professionals, we certainly have no interest in improving the well being of our patients by increasing fruit and vegetable intake. The only thing we care about is the number of the scale. Thanks for clarifying your priorities for us, Ted.
July 24, 2018 at 4:26 am, Ted said:
I’m not so sure that your assumptions are correct about the effects of glib dietary advice, Paul. But thanks for sharing your opinions.