Carbs Be All Hard to Understand

Normally I don’t really address diet and nutrition related stuff. It’s really outside my scope of interest, but rarely there comes a perfect storm of stupid and publicity that gets my attention and makes me want to rant a little.

This is one of those occasions. I came across this article posted on a forum I read, and man does it deserve a thrashin’.

The first thing you’ll notice is that it’s a departure from the standard low-carb craze that’s making the rounds. This is different, actually encouraging people to eat carbs. And really, that is a breath of fresh air what with Gary Taubes’ book making the rounds.

A lot of the low-carb nuts really have no understanding of basic thermodynamics, let alone the relevant physiology, which is why they adhere to their simplistic ideas about insulin (and thus CHO intake) being solely responsible for obesity. Yeah, no.

So anyway, I see this article and I think maybe somebody’s got a clue. Oh was I ever disappointed.

This article is just a little bullet-point piece from a Celebrity Nutritionist, those little sound-bites that we all know are so informative. Sad as it is, anybody that’s on a mass-media TV show and talking about nutrition or exercise has about an 85% chance of being completely unqualified to talk about the subject, so I was on guard from the get-go.

And boy do I love being proven right. This nutritionist did something that takes considerable skill: she completely opposed the low-carb nuttery with the same arguments the low-carb nutters use.

Let’s go one by one.

1. Combine carbs with protein. This one is actually good advice. Protein will influence satiety and fullness more than either fat or carbs, mainly because it digests much slower. Because of that, any carbs eaten with a protein-containing meal are going to digest slower as well, and thus have less of an impact on blood sugar levels. However you can already see the looming specter of the Glycemic Index and insulin levels, foreshadowing the horrors to come.

2. Eat carbs more often. Aaaaaaaaaaaand right here the train completely derails.

“Eating a carb-protein meal 4 times per day rather than 3 helps keep blood sugar levels stabilized. This keeps the metabolism firing and energy levels high.”

Yeah, no. There is something to avoiding blood sugar crashes so as not to set off a hunger signal, but that’s only part of the puzzle. If you eat three decent-sized meals a day and you aren’t just mainlining sugar for any of them, you’re really not going to get crashes. Meals with a decent mix of protein, fat, and carbs will just not do this.

While there is some evidence of increased fat oxidation with frequent eating, the people focusing on this neglect to account for the metabolic costs of eating larger meals. The long and short of it is that frequent feedings will increase fat oxidation, but they total energy cost isn’t necessarily greater than the thermic effect of food (TEF) that comes from eating fewer, larger meals. A bigger meal takes more time and energy to digest; this energy cost will offset any reduction in fat oxidation.

Given the same calorie intake (IMPORTANT) distributed across greater or fewer meals, the net result at the end of the day is no difference. You can’t beat thermodynamics.

“Research has demonstrated that regulating blood sugar levels regulates hormonal secretions which results in optimal fat burning.”

This is a half-truth. Insulin tends to work in opposition to catecholamines (epinephrine and norepinephrine), which do stimulate lipolysis (release of fat from fat tissue) and fat oxidation, so from that standpoint regulating blood glucose sounds like a good idea.

However, there’s a confounding issue: any meal you eat will stimulate an insulin response unless it’s only fat. Yes, protein does stimulate insulin, and it doesn’t take very much to negate that lipolytic effect.

That’s why fat oxidation between small frequent meals and TEF from larger infrequent meals balances out. Eat frequently and you elevate fat oxidation at the cost of TEF. Eat infrequently and you get a bigger insulin spike which reduces fat oxidation to a larger degree, but TEF is increased because of the bigger meal.

Given an equal energy intake, it balances out over a 24-hour period.

“Not only this, but carbs must be present in the system for the chemical process of fat-burning to work.”

AMPK is more than capable of increasing fatty acid oxidation without carbs, and in fact it does just that when blood glucose is low.

Or to put it another way: this must be why all the people rescued from Auschwitz were fat, right?

3. Eat carbs at every meal. Not much to say about this one really. It’s relying on the same notion that people will experience violent hunger from carb crashes if they aren’t eating every two hours or whatever the Bro-wisdom says.

Satiety is regulated as much by the digestive tract, if not more, than it is by blood sugar levels (and the two are related anyway). Let it suffice to say that hunger is better controlled with protein and fat meals, and your body’s not going to sit there full of steak and tell you to go eat a bag of cookies. Whether you eat carbs with that meal or not isn’t going to terribly influence things.

This deserves special mention though:

“This is because the brain needs the glucose from carbs for fuel and if it doesn’t get more within 4 or 5 hours, your body has no choice but to break down lean body tissues (like muscles) for fuel.”

Oh come on, even the low-carb guys get this right. If you’re eating enough protein you won’t be breaking down anything because the circulating amino acids will cover any AA oxidation. If she’s got proof of net protein loss occurring in skeletal muscle as she describes, given sufficient dietary protein, I’d like to see it (hint: it doesn’t exist).

And there’s also that little matter of ketosis which can cover the brain’s energy needs in conditions of carb deprivation.

4. Eat carbs late at night. Same “fueling the metabolism” stuff. Just no.

While I think the “no carbs at night” guys are overblowing the matter, I don’t see any real advantages to going out of your way to eat carbs, either. If you’re in a net calorie deficit for the day, it doesn’t really matter what you eat.

Now we get to the real kicker, the point that really motivated me to write this.

5. Don’t overdo it at one time.

“Your body isn’t a cash register. It doesn’t add up your total at the end of the day. It only cares how much you eat at a single meal. If you eat one entire large deep-dish pizza, your body converts the carb overload to fat storage. However if you only eat two light slices now and two slices for dinner 4 hours later, you won’t overload the bloodstream with glucose at one time, thus you will keep your fat-burning going.”

Yeah, about that, uh, actually it does account for total calorie balance. It doesn’t sit there and add up everything you ate from midnight to 11:59 like an accountant (because that’s a really stupid thing to believe, if she thinks anybody’s actually saying that) but energy entering a system has to balance out the energy leaving the system. Doesn’t matter how that energy leaves the system or when it leaves, this balance must exist. That’s not a property of our bodies. It’s a property of the universe.

Really, let that sink in. Physicists have known about thermodynamics for quite awhile, and we’ve never once, in all of human science, found an exception to that. Energy in = energy out. If it didn’t work that way, we’d have perpetual motion machines and no looming energy crisis.

Her point about eating the pizza all at once vs. spreading it out is exactly what I said before about TEF vs. fat oxidation. When she says that a big meal increases insulin and causes fat storage, she’s absolutely right. That does happen after a meal. So why am I bitching? Because she’s conveniently leaving out a key piece of information. What happens if this person doesn’t eat again for the rest of the day, and that pizza was 500 kcals under this person’s calorie need for the day?

All that fat that was stored is coming right back out into the bloodstream and it will be burned up for energy. The calorie balance will win out every single time. Look at it this way: you don’t put your paycheck in your savings account when you can’t pay the rent. If the bills aren’t covered, it makes no sense to put the money away.

She’s not considering the big picture, only the micro-level slices of physiology, which is where the reasoning falls to pieces. Just so you don’t think I’m just making things up, here’s a little science to back me up. This isn’t just a Pubmed abstract – the entire paper is available online at this link:

Astrid J. Smeets and Margriet S. Westerterp-Plantenga (2008). Acute effects on metabolism and appetite profile of one meal difference in the lower range of meal frequency. British Journal of Nutrition, 99, pp1316-1321
doi:10.1017/S0007114507877646

For those too lazy to read or not well-versed in deciphering research, they tested two groups: one eating two meals/day vs. another eating three meals/day, controlled for the same number of daily calories, to see if it had any effect on fat balance or energy expenditure. The result? No difference in 24-hour energy balance between the two.

This is just confirmation of what I said before: frequent small meals do increase fat oxidation, but larger less-frequent meals increase the energy cost via TEF. At the end of the day, the feeding pattern doesn’t matter as long as the calories are accounted for. If the net energy intake is less than the net expenditure, weight goes down and fat is lost.

Now as far as satiety, frequent feedings do seem to show some advantage in that area. Satiety is important, considering that you are the one controlling your food intake. You aren’t in a calorimetry chamber with researchers giving you meals. You have to make your own food choices, and being not-hungry can help with making the right choices.

However, a big meal that fills you up for six hours isn’t necessarily worse than grazing on the same number of calories  over the same period of time. The trick is to find a strategy that allows you to eat less. Quibbling over the details won’t do much.

I want you to realize that some of these points aren’t inherently bad advice. What I’m complaining about is the complete lack of understanding behind the recommendations. The notion that you must eat frequently to “keep your metabolism stoked” is garbage. There are good reasons to do so, perhaps, such as appetite control, but there’s no inherent physiological reason to do so.

Of course you see the problem there. When you’re making claims based off science, and your understanding of that science is flawed or non-existent, then you can make even more fundamental errors.

And of course we can’t forget the Guru Syndrome striking yet again. When somebody goes on TV and proclaims herself to be an expert, yet can’t understand basics of physiology (or high school physics for that matter), I really want to know 1) why that person is on TV and 2) why she’s proclaiming herself to be an expert.

I never seem to get an answer.