Tag: nutrition

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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I was reading a profile of British historian Lucy Worsley in the New Yorker last night, in which the writer (Lauren Collins) takes part in the authentic re-enactment of the meal eaten by King George on February 6, 1789:

THEIR MAJESTIES DINNER

Soupe barley

4 chickens roasted

3 pullets minced and broiled

7 3/4 mutton collop pyes

6 perch boiled

2 breasts of lamb a la pluck

2 salmic of ducks

13 loin veal smort

(And a partridge in a pear tree, presumably.) The article is both fascinating and funny, but the culinary payoff after an enormous amount of work ends up being a bit anticlimactic:

If every age has its sounds and smells, it also has its flavors. The taste of 1789 can be a dog whistle to modern palates… “You’ve had your tongue burnt off by a Mexican chili, and you’ve been eating sugar cookies since you’ve been able to stand [says Marc Meltonville, co-head of the Historic Kitchens team;] if something’s subtle, sweetened with rose petals, how are you going to be able to taste it?”

This made me think of the long-running and bitter debate about the “right” amount of salt consumption, and how tastes are formed. Just this morning, the New York Times reported on a neat new study suggesting that the amount of salt you’re fed as an infant determines your taste for it in later life. But taste for salt is also somewhat plastic. When my wife and I started eating together, her taste for salt was dramatically higher than mine. Now, a few years later, our tastes have sort of met in the middle. She no longer adds as much salt to food as she used to; but when I visit my parents, I find that I now need to add salt to dishes that I loved for many years with no added salt.

And I still struggle to reconcile all this with the widespread message that we’re eating wayyy more salt now than we used to (and thus salt is responsible for the current epidemic of hypertension). As I wrote last year about a study by Harvard’s Walter Willett:

He and a colleague reviewed studies between 1957 and 2003 that measured sodium excretion in urine — a very accurate way of determining salt intake that gets around the difficulties in figuring out exactly how much salt is in your food. They found two main things: (a) sodium intake averaged about 3,700 mg per person per day, which is way higher than the upper recommended limit of 2,300; and (b) it essentially hasn’t changed in the half-century studied.

Interestingly, these results agree almost exactly with similar reviews of studies from 33 different countries: salt intake is high, and it hasn’t changed in recent memory.

And Henry VIII, according to Worsley in the New Yorker piece, ate 20 grams of salt each day!

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

***

Those of you interested in nutrition may already be following the online debate between Gary Taubes and Stephan Guyenet — back in August, Guyenet critiqued Taubes’s carbohydrate-insulin hypothesis, and now Taubes is returning the favour by critiquing Guyenet’s food-reward hypothesis. I’m not going to get into the nitty-gritty of the debate here, except to say that I think it’s a mistake to frame this debate as an “either-or.” Despite Taubes’s insistence to the contrary, the two ideas can coexist — and even if they do, I suspect they still don’t add up to the “whole truth” about obesity. Here’s one reason why.

In one of his recent posts, Taubes makes the distinction between body-centred and brain-centred theories of obesity (or you can think of it as physiology vs. psychology, one of his commenters points out). Taubes believes obesity originates in the body:

In this paradigm, specific foods are fattening because they induce metabolic and hormonal responses in the body — in the periphery, as its known in the lingo — that in turn induce fat cells to accumulate fat. The brain has little say in the matter.

Leaving aside the precise mechanism, I largely agree with the idea that regulation of calories in and calories out isn’t under the conscious control of the brain. And I’m pretty sure Guyenet would agree too. But I’m not quite ready to conclude that the brain plays no role.

This is a figure from a study published in the Archives of Pediatrics & Adolescent Medicine in 2009, from researchers at Penn State (no wisecracks please). The text is freely available here. The study followed 1,061 children, who were tested at the age of 3 for self-control (the length of time they were able to refrain from playing with a fun toy after being asked not to) and then again at the age of 5 for delayed gratification (the classic Marshmallow Test, which I’ve written about before, except using M&Ms, animal crackers or pretzels: they could have a small amount anytime, or a larger amount if they waited 3.5 minutes). Then their BMI was tracked until their turned 12.

The results are pretty clear: doing well on either or both of the impulse-control tests predicts less weight gain nine years later. So the question is: how can a test that involves (not) playing with a toy when you’re 3 years old predict future weight gain, if the brain has no say in weight gain?

Let me be absolutely clear: I don’t think “better impulse control” will play any useful role in weight loss for the vast majority of people. Once you’re overweight, I suspect physiology totally swamps psychology in most cases. But if you’re looking for an overall understanding of the mechanisms of weight gain and loss — and if, like Taubes, you insist that the correctness of your theory means that all alternate ideas must be 100% incorrect — then I believe you can’t ignore the brain (and its interactions with the modern food/physical activity environment) completely.

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

***

The classic syllogism of “nutritionism” goes something like this:

1. Eating food A makes people healthy.
2. Food A contains nutrient X.
3. Therefore we should isolate nutrient X, manufacture it in powder form, and ingest it large quantities to become healthy.

This seems pretty logical, and I certainly wouldn’t have questioned this basic mode of thinking a decade ago. And of course the approach has had many successes — taking vitamin C really does ward off scurvy if, for whatever reason, you’re subsisting on a diet devoid of vitamin C. But when we shift from “correcting deficiencies” to “enhancing health,” the approach seems to sputter, as people like Michael Pollan have argued.

The question, from my perspective, is: Why? Why do so many studies find that taking an isolated nutrient fails to reproduce the benefits observed from ingesting that nutrient in the context of a whole food (or, perhaps even more importantly, a whole meal or whole dietary pattern)? There are obviously many factors, such as the rate at which the nutrients are absorbed, and synergies between different nutrients in the food (a possible explanation for why nitrites are “good” when they from spinach and beets but “evil” in the context of fatty hot dogs).

A new study published last week in Neuron (press release here, abstract here) offers another clue. The study looked at the activation of “orexin/hypocretin” neurons in the hypothalamus, which “regulate energy balance, wakefulness, and reward.” It has long been known that glucose levels in the brain reduce the activation of these neurons. Researchers at the University of Cambridge tested how they responded to protein and fat, and found that certain amino acids increase the activation of the neurons, while fatty acids have no effect.

Okay, so the brain responds to macronutrient levels in the body. Cool. Carbs turn this particular neural signal up, and protein turns it down. And if you eat both protein and carbs at the same time, you’d expect that the net result will be the sum of the two signals. But that’s not what the researchers found. The combined protein-and-carb signal was a nonlinear combination of the two individual signals — meaning that these neurons were, in effect, responding to the protein-to-carb ratio rather than amounts. As the researchers put it:

In summary, our data show that the activity in the orx/hcrt system is regulated by macronutrient balance, rather than simply by the caloric content of the diet.

The bottom line: if you try to understand how this particular aspect of human physiology works by breaking food down into its constituent nutrients and testing them one by one, you’re doomed to failure because its response to individual nutrients is different from its response to combinations of nutrients. Which leads to a corollary: if you try to create a healthy diet by assembling a collection of pills and powders, you’re almost certainly sacrificing some of the synergies present in real foods.