"There is an inflexible law of physics — energy taken in must exactly equal the number of calories leaving the system when fat storage is unchanged. Calories leave the system when food is used to fuel the body. To lower fat content — reduce obesity — one must reduce calories taken in, or increase the output by increasing activity, or both. This is true whether calories come from pumpkins or peanuts or pâté de foie gras.

To believe otherwise is to believe we can find a really good perpetual motion machine to solve our energy problems. It won’t work, and neither will changing the source of calories permit us to disobey the laws of science."

A calorie is a calorie.

However, carbohydrates are addictive to many people.

So it's not that they're getting calories from carbs. It's that eating carbs makes many people want to eat more carbs.

This is a chemistry problem, not a physics problem. :)

100% agree. Most people fail to make that distinction.

I lost 25 pounds in 3 weeks.

I ate an all-protein diet and drank 3 liters of water a day. I did not eat anything but lettuce, beef, chicken, eggs or unsalted cashews for 21 days.

I do believe that a high protein diet makes you feel full faster.

Not sure if that's psychology, biology, or chemistry.

The real question is why so many people have trouble staying on a true protein and fruit/vegetable diet.

Also, not sure if that's psychology, biology, or chemistry.

Because in the wild, we had no choice but to eat a high fat, moderate protein, high fiber, whole food diet. The massive temptations that we are subjected to every day have no historical precedent. It's as if all men were tempted with free sex from beautiful women on every street corner all of the time. It takes iron discipline to resist.

There are problems with the thermodynamic 'inflexible law of physics' model of human nutrition.

As Adam notes, some foods tend to put people on a path toward more consumption. Calorie selection matters there.

As the recent JAMA study suggests, some foods may trigger more activity/calorie-use. So again calorie selection matters.

So if carbs trigger sooner food cravings, *and* depress overall rates of caloric consumption, perhaps there's another factor more than just 'calorie count': something in the realm of signalling/equilibrium, rather than just physics.

I would also add that there is no requirement that every potential caloric chemical 'ingested' by the body be either burnt for energy or stored as fat.

Swallow a wood chip. Though it has a precisely measurable 'caloric' potential if fully combusted, the human digestive system doesn't set things on fire, so those calories are irrelevant. They're passed out of the body.

But even short of fire, plenty of purely biochemically-powered organisms can derive energy from a mammal's passed waste. So there's a continuum of digestive processes to use offered calories. And maybe, an organism can dial up or down its usage of substances passing through.

Throw a handful of flour into the air, and light a match. (OF COURSE DO NOT REALLY DO THIS!) There will be an explosion. You would be hard-pressed to make use of just a small wanted, measured portion of that energy, conserving the rest for later. It's all-or-nothing. Alternatively, grab a candle and light it. It burns slow and long. As soon as you no longer want its output, the reaction can be stopped, and the remaining potential energy stored or discarded. It's a process that's amenable to marginal/feedback-control.

And see what I did there? The flour is a starch, and the candlewax a fat. Some chemical processes can be inherently more regulable by biological systems than others. If the body can choose to graze on fats/proteins, but must gorge itself on carbs, then again calorie source selection matters more than 'inflexible law of physics' net tallies.

This is the main method used to measure calories.

http://www.dummies.com/how-to/content/how-nutritionists-measure-calories.html

Note that the measurement process takes place ENTIRELY OUTSIDE THE HUMAN BODY. There's your physics.

It seems like Dr Hirsch also did experiments involving liquid diets with precisely measured amounts of carbohydrate and fat calories. Three issues:

* Liquid diets != food

* As far as I can tell from his description, there was no variation in the amount of protein in these diets. There may not have been any protein in these liquids.

* I'm assuming that the users were not allowed to eat more or less of the liquid food based on how hungry they felt, since the point was to strictly control their caloric intake while varying the fat and carbohydrate composition.

Dr Hirsch began with the assumption that a calorie is a calorie, and he designed a series of experiments that "proved" this is so. What he did NOT prove or disprove is that people lose more or less weight on high-protein diets in the real world. In that sense the writer of the headline here is at fault.

I have to say as someone who eats a LOT of vegetables, that I could believe the calorie count obtained by burning them in an oxygen chamber is different from the amount of energy I derive from eating them. Not only can you burn fiber for fuel that your body cannot digest... but the "jillions of hormones" that Dr Hirsch so cavalierly glosses over -- and also microflora -- have a powerful effect on how your body decides to deal with food on a daily basis.

After my traumatic brain injury I learned firsthand how little we provably know about endocrinology, and I've been fascinated by recent research into human microbiota. These are real frontiers of knowledge right now, and very exciting! I think in 20 years we will look back on this "calories are calories" thing and laugh at how primitive our collective knowledge was.

From personal experimentation, I am a backer of more protein and more vegetables. I think you hit the key question, Adam, not whether the high protein diet is better...but that why so many fall off it so easily. I believe it is likely tied to the larger issue of self-discipline that we as a people currently struggle with.

You don't need self-discipline when you're able to eat liberal amounts of fat at every meal and still lose fat and gain muscle...

This guy is a physician, not a physicist. The human body is not a closed system. It is an open loop thermodynamic system operating far from equilibrium. Three simple examples to shoot holes in his theory:

- Go hang out in freezing cold water. You'll burn calories because of the effort to maintain your body temp. Same way, if a different diet or lifestyle slightly alters your metabolic rate, or operating temperature, it'll alter how many calories you burn. And different foods will affect you differently.

- Some food sources (carbs) make you hungrier. Some make you more sated (fat)

- Some food sources poison you (fructose) and make you sleep longer (carbs). Others keep you awake (protein).

What you eat matters far more than how much you eat. I listened to guys like this until I was 30 and struggled with obesity. When I switch to a whole-foods high-fat diet, I'm fit as a fiddle. Almost no exercise needed.

Delete this guy, delete the NY Times. He doesn't look in great shape anyway. Read Gary Taubes, and follow the Archevore:

http://www.archevore.com/get-started/

A calorie from fructose is poison. A calorie from glucose, lactose, galactose will make you hungrier and lead to another calorie. A calorie of fat will make you feel more sated. A calorie from protein is easier to store as muscle. A calorie is not a calorie. A calorie just happens to be a thing that we managed to measure in the 19th century by setting fire to food. The human body is far more complex than that.

More than 70% of the total daily energy consumed by all people in the United States comes from foods such as dairy products, cereals, refined sugars, refined vegetable oils and alcohol, that advocates of the Paleolithic diet assert contributed little or none of the energy in the typical preagricultural hominin diet.[10] Proponents of this diet argue that excessive consumption of these novel Neolithic and Industrial era foods is responsible for the current epidemic levels of obesity, cardiovascular disease, high blood pressure, type 2 diabetes, osteoporosis and cancer in the US and other contemporary Western populations.[10]

http://en.wikipedia.org/wiki/Paleolithic_diet

One more clarification: in a whole foods high fat diet, the fats are nuts and avocados, right? Anything else?

Coconut, eggs (yolk is great), butter, beef tallow, coconut oil, ghee, pork fat, olive oil, macadamia oil, whole cream, hard cheeses (in moderation)...there are more. Problem is, refined vegetable oils are pretty much impossible to avoid if you eat out. They're everywhere.

Yes, that's a big problem. It sounds like the key is to be very careful in restaurants.

Effective for WHAT, is the question, and at what body fat percentage.

People who are obese can make pretty much any proactive change in their diets and see weight come off.

Those in the 25+ % body fat range can simply restrict carbohydrates or total calories and see fat loss.

So yeah, it does SEEM to be as simple as calories in / calories out. It gets a bit dicier when you get into the under-25% body fat area.

People under 25% body fat often need to build muscle in order see more fat loss, and/or restrict carbohydrates further.

But the point that seems consistently lost on the medical community is that metabolism is TRAINED.

A HIGH protein diet -- rather than one high in fat and moderate in protein -- will not be a good idea in the long run for any of these populations. If you constantly eat high protein and don't get more of your calories from fat, you end up burning muscle for fuel in times of caloric deficit.

Contrast that with what happens on a high-fat / moderate protein diet: the body becomes "fat adapted" and more likely to burn body fat for fuel in times of caloric deficit.

In this way, a calorie is NOT just a calorie. And a high-protein diet is a sure way to lose a bunch of muscle, which is not what 99% of people want.

Not all diets are good for everybody, it must be said. But the up/down-regulation of the glycolytic cycle and the suppression or elevation of insulin levels are known quantities, representing basic chemical truths about the human body -- EVERY human body.

(I realize I was commenting mainly on the headline and not on the article, but headlines matter. People think Atkins is about "high protein" when in fact it works best with about 70% of calories from fat.)

Also: goddamn it is annoying to see people obsessing over "weight loss". Nobody wants to lose weight, they want to lose FAT.

Here's an easy way to lose weight: cut off your arm.

You make several good points.

Just for clarification: a high fat moderate protein diet is still low carb, right?

A low carb diet is almost by definition high fat. The body can only handle so much protein before toxicity hits. I don't think a low-carb, low-fat diet is possible.

The source of the fat is all-important. Rancid seed oils are horrific, right down there with sugar or worse. Fat from a steak or an avocado are great.

Whole, natural foods. High fat. Medium protein. Low simple carbs (veggies are complex carbs). Moderate to low nuts, dairy, wine, fruits. No foods from a package that sits at room temperature on the shelf, or from a can (if bacteria won't eat it, why should you?). Watch the pounds melt away.

What really strikes me as I read what you've written, Naval, is that almost everything produced by the food and restaurant industries is not, in fact, food.

It's stuff with calories that people put in our mouths.

It's going to take a while to internalize why so many systems have been set up as obstacles to eating the right way.

It's very simple, actually. Almost everything designed and served by restaurants and supermarkets is made for your mouth, not your body. Almost everything designed to seem healthy is made for brandability, mass production, and differentiation. No food manufacturer or restaurant can make money by telling you that the best things are whole, unprocessed, non-patentable or trademarkable, undifferentiated meat and vegetables.