How many meals a day should you eat?

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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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In response to a recent reader e-mail:

My question is the following: is it better to eat three meals per day or is it better to eat several small meals throughout the day? I am currently weight training a few times per weeks and I am also trying to lose some weight. Ideally, I want to lose some fat while also gaining some muscle.

This debate has bounced back and forth since at least the 1960s (when some key papers were published in Lancet and the American Journal of Clinical Nutrition). The latest take comes in a study by researchers at the University of Ottawa that will appear in a forthcoming issue of the British Journal of Nutrition. The basic idea is that eating more frequently might keep you feeling more full, possibly by preventing big swings in the gut hormones that influence hunger:

Increased feeding frequency has often been proposed to convey favourable effects on body weight, adiposity and energy intake, but controversy persists. It has been hypothesised that the favourable effect of increased meal frequency (MF) could emanate from a more sustained release of gastrointestinal hormones; however, more studies are needed to confirm this postulation.

In this study, they put 16 obese volunteers on diets with identical caloric deficits for eight weeks. Half of them ate three meals a day, while the other half at three meals plus three snacks. The results: no difference. Or, in science-ese:

The premise underlying the present study was that increasing MF would lead to better short-term appetite regulation and increased dietary compliance; furthermore, it was hypothesised that these predicted beneficial effects of increased MF could have resulted from more favourable gut peptide profiles, potentially leading to greater weight loss. Under the conditions described in the present study, all three hypotheses were rejected.

Now, only a fool would think that, after nearly half a century of conflicting results, the newest study must be the truest. This is just one more data point. But it suggests to me that there isn’t compelling evidence either way — so the choice is up to you. Personally, I snack.

(Thanks to Jim for the question, and to this NYT article for the pointer.)

Why harder is better than longer for post-weight-loss exercise

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)

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I posted earlier this month on “why weight loss isn’t just calories in minus calories out,” which led to an interesting discussion on the ways in which the body tries to prevent itself from gaining or losing weight. On that topic, I came across an interesting study published earlier this year in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, from researchers at Columbia University. The gist: it’s the efficiency of our muscles, on a cellular level, that conspires to hold our weight steady.

It’s well-known that, if you lose weight, your metabolism slows down to burn fewer calories. (That’s why, as a recent JAMA paper pointed out, eating one less 60-calorie chocolate-chip cookie per day won’t allow you to keep losing weight forever. Instead, if exercise and other factors are kept constant, you’ll plateau after a few years at a weight six pounds lighter.) Part of that is because, as Phil Koop pointed out, “adipose tissue has a metabolic cost.” Or as the JAMA paper puts it:

A person who consumes an extra cookie every day will initially experience weight gain, but over time an increasing proportion of the cookie’s calories will go into repairing, replacing, and carrying the extra body tissue.

But the Columbia paper makes it clear that the extra tissue, on its own, isn’t enough to explain the changes in how many calories you burn:

Maintenance of a body weight 10% below “usual” for a lean or obese individual is accompanied by a reduction in systemic energy metabolism (~300–400 kcal/day less than that predicted solely on the basis of changes in body weight or composition), neuroendocrine function (decreased circulating concentrations of leptin and of bioactive thyroid hormones), autonomic nervous system physiology (decreased sympathetic nervous system tone and increased parasympathetic nervous system tone), and behavior (decreased satiety) that act coordinately to return body weight to its initial level.

To figure out where these missing calories go, the Columbia group has been doing extremely careful experiments that involve checking volunteers into an inpatient research clinic for several months at a time, and feeding them only a liquid diet (40% corn oil, 45% glucose, 15% casein protein, by calories) so they can precisely monitor energy intake. They control the amount of feeding to make the subjects gain or lose 10% of their body mass, then study the changes to their metabolism. Pretty neat stuff.

Anyway, the major finding of this new study is that “skeletal muscle work efficiency” changes dramatically when you change your body weight. It’s not just because your muscles have less weight to carry around — it seems to have more to do with changes in the ratio of enzymes that determine whether the muscle burns carbohydrate or fat. When you lose weight, your muscles get more efficient — which seems like a good thing, except that it means you burn significantly fewer calories when you move around, which pushes your weight back up. The opposite happens when you gain weight: your muscles get less efficient.

So what’s the take-home (other than “Try not to gain weight, because it’s really hard to lose once you do.”)? Because the ratio of carbohydrate-to-fat utilization depends on the intensity of physical activity, there’s reason to believe that the efficiency changes are only relevant at very low intensities — corresponding to the activities of day-to-day life as opposed to “exercise.”

From a therapeutic standpoint, exercise post-weight reduction might be more effective at higher workloads, i.e., that the weight-reduced individual might “escape” this increased efficiency by altering the intensity of exercise even without necessarily increasing the work performed.

In other words, exercise harder rather than longer might be the most effective strategy for keeping weight off.

Live Q&A: Thursday, March 25, 3 p.m. EST

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)

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Just a heads-up that I’ll be doing a live web-chat Q&A on the Globe and Mail website tomorrow (Thursday, March 25, 3 p.m. EST), taking questions about running, training and preparing for races. Feel free to pop by with any questions you’ve got — the session will last an hour, and will be located at this link.

The secret of Kenyan success: it’s not the hemoglobin

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)

***

April’s issue of Medicine & Science in Sports & Exercise brings another in the long line of studies trying to figure out why Kenyan runners are so much better than the rest of the world (other than some of their East African neighbours). As researchers from the universities of Bayreuth and Tubingen in Germany write:

Possible reasons for this performance superiority range from the physiological to the biomechanical, social, and economic, but none of them appears to be exclusively responsible.

Earlier studies have found that elite Kenyan runners have better running economy than elite Caucasian runners — in other words, they require less oxygen to run at a given level of effort. One theory is that Kenyan muscles somehow use oxygen more efficiently, but studies of muscle morphology and function haven’t been able to pick up any significant differences. Another possibility is that, thanks to adaptations from having ancestors living at altitude for 100,000 years, Kenyans are able to transport more oxygen in their blood to fuel the muscles.

To investigate this possibility, the new study measures total hemoglobin mass (tHb-mass) and blood volume (BV), the two factors that predominantly determine oxygen transport. They compared 10 Kenyans with an average 10K time of 28:29 who were staying in Germany for six weeks with a group of 11 German runners with average 10K time of 30:39. Cutting straight to the chase: when the Kenyans arrived in Germany from altitude, their total hemoglobin mass and blood volume per kilogram of body weight were essentially identical to the Germans. As the six weeks in Germany progressed, the Kenyans got fatter (added 3 kg of bodyweight, including 1 kg of fat), and their hemoglobin and blood measures got worse. The conclusion:

The oxygen transport of the blood, that is, tHb-mass and BV, cannot explain the superior endurance performance of Kenyan runners. All of these parameters are in the same range when compared with those of elite German runners, and tHb-mass even deteriorated after adaptation to near sea level.

Jockology: some (but not all) pre-run stretching slows you down

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)

***

I posted last month about a new study on how static stretching before your run makes you slower and less efficient. To find out more about the study, I got in touch with the lead author, FSU’s Jacob Wilson. The result is this week’s Jockology column:

For years, researchers have been finding that the more flexible you are, the less efficiently you run – a message that tradition-bound runners have been reluctant to hear. Now, research to be published later this year in The Journal of Strength and Conditioning Research makes it clear that some (but not all) prerun stretching makes you slower. [read the whole article]

The most significant new piece of news in the article is that Wilson and his colleagues have just finished a follow-up study, in which they used the exact same protocol to study dynamic stretching. They’re still completing the analysis, but the results appear to show no significant decrease in performance for pre-run dynamic stretching. This means that you can still get your flexibility fix before a run without compromising performance — you just need to use dynamic stretches instead of static ones. (Some examples, with illustrations, are provided in the Jockology article.)

Drilling deeper into the dynamic stretching data, Wilson said it appeared that the most experienced runners weren’t affected by the pre-run stretches. Less experienced and less fit runners, on the other hand, still saw a bit of performance decline, probably because the unfamiliar stretches fatigued them a bit. So make sure you practice these stretches before trying them in a race situation. (This last stuff is very preliminary, so it may not be statistically significant — we’ll have to wait until the study is published to see.)