The Physics Diet

Want to lose weight? Easy! Just remember the first law of thermodynamics: conservation of energy. Oh, and you'll have to not mind being hungry.

By Richard A. Muller

Technology for Presidents

MIT, November 14, 2003

link to article

Here’s an old joke. The dairy industry hires a physicist to improve milk production. After several weeks, he’s ready to lecture about his progress. He draws a circle on the blackboard and says, “Consider a spherical cow….”

I’ve told this joke many times, but nobody ever laughs—except other physicists. For the rest of you, I should explain that it is self-deprecating humor. It makes fun of our penchant for oversimplification.

This month I want to talk about diet and exercise for weight loss, and I’m going to oversimplify on purpose. Consider a spherical physicist….

Most dieters are so concerned about second-order effects, such as daily fluctuations in weight and changes in metabolism, that they lose track of the first law of thermodynamics: conservation of energy.

Want to lose a pound of fat? You can work it off by hiking to the top of a 2,500-story building. Or by running 60 miles. Or by spending 7 hours cleaning animal stalls. (It is amazing what scientists have actually measured. This last example is tabulated in the book Exercise Physiology by G. Brooks and T. Fahey.)

Exercise is a very difficult way to lose weight. Here’s a rule of thumb: exercise very hard for one hour (swimming, running, or racquetball)– and you’ll lose about one ounce of fat. Light exercise for an hour (gardening, baseball, or golf) will lose you a third of an ounce. That number is small because fat is a very energy-dense substance: it packs about 4,500 food calories per pound, the same as gasoline, and 15 times as much as in TNT.

If you run for an hour, you’ll lose that ounce of fat and also a pound or two of water. By the next day, when you’ve replenished the water, you might think, “the weight came right back!” But you’d be wrong—you really did lose an ounce. It is hard to notice, unless you keep running every day for a month or more, and don’t reward yourself after each run with a cookie.

There is a much easier way to lose weight, as we can learn from the first law of thermodynamics. Eat less.

A reasonable daily diet for an adult is 2,000 food calories. That’s 8.36 megajoules per day, or about 100 joules per second—in other words, 100 watts. Most of that ends up as heat, so you warm a room as much as a bright light bulb. Cut your consumption by 650 calories per day and you’ll lose a pound of fat every week. Most diet experts consider that a reasonable goal. Don’t drop below 1,000 calories per day, or you might get lethargic. But at 1,350 calories per day, you can easily maintain an active life.

Of course, there is a catch. You’ll be hungry.

It’s not real hunger–not like the painful hunger of starving people in impoverished countries. It’s more of a mild ache, or an itch that you mustn’t scratch. To be popular, a diet must somehow cope with this hunger. Weight Watchers does it with peer support. The food pyramid does it by encouraging you to eat unlimited celery. Some high-fat diets satisfy all your old cravings—and figure you’ll eventually cut back the butter you put on your bacon.

Last April, I had once again grown out of my belt. I wasn’t grossly overweight: 205 pounds in a six-foot, one-inch body. That wouldn’t be bad for a football player, but I’m 59 years old, and the excess pounds weren’t in muscle. I had gained a pound a year for several decades. I felt heavy and old. I decided to try conservation of energy. I gave up lunch and snacks.

How to cope with the hunger? I attempted to enjoy it. I thought of the movie Lawrence of Arabia, in which T.E. Lawrence says, “The trick…is not minding that it hurts.” I told myself that the mild ache was only the sensation of evaporating fat. That interpretation has some basis in physics. When you lose weight, most of your fat is converted to the gases carbon dioxide and water vapor, and so you get rid of fat by breathing it out of your body.

Physics works, and I lost weight. By August, I was down to 175 pounds, a 30-pound drop. My belt went from 42 inches to 36 inches. My Zen-like approach to hunger also worked; I found myself declining offers of chocolate cake because I didn’t want to lose the sensation of evaporation. I didn’t change my level of activity, and managed to maintain my diet while taking trips to Cuba and Alaska—and during a week-long backpacking excursion in the Sierra Nevada. A key innovation: I kept up the social aspects of lunch, without eating. I watched others gobbling cheeseburgers, while I sipped diet cola. It really wasn’t that hard to do. And the mild afternoon discomfort was compensated by several positive developments. Dinner became truly wonderful. I hadn’t had pre-dinner hunger for decades. A sharp appetite turns a meal into a feast. No more cheese “appetizers” for me.

Moreover—and this may sound silly coming from a physicist—I was surprised that I began to feel lighter. I no longer walk down streets—I float. Distant stores seem closer. And my knees have responded to the lighter load. Their aching, which I had mistakenly attributed to aging, went away.

Food is instant gratification. And fast-food chains and gourmet restaurants serve tasty food at remarkably low cost. It is a situation unprecedented in history and unanticipated by our genes. No wonder we are overweight.

Anybody can lose weight. Energy is conserved. Just stop scratching that itch. Of course, you’ll have to sacrifice instant gratification. Is it worth it? You decide. Food is delicious and cheap. You might reasonably choose to take advantage of this unique historical circumstance, and decide to be fat.

It’s been seven months since I started my diet, and two months since I left it. I’ve begun eating a light lunch, and having an occasional small snack. I’m still at 175. But I never want to lose the delicious edge of hunger before dinner, or the floating sensation when I walk. Moving takes less energy now, so I have more energy. I no longer feel like a spherical physicist. And for losing weight, dieting sure beats cleaning animal stalls.

Richard A. Muller, a 1982 MacArthur Fellow, is a physics professor at the University of California, Berkeley, where he teaches a course called “Physics for Future Presidents.” Since 1972, he has been a Jason consultant on U.S. national security.

What's next self-flagellation? Yes, after a while the cat'o'nine tails will start to feel pretty normal.... Or perhaps a shirt of hair.... This is an S&M approach to food.

This fellow is describing the euphoria of starvation.... next thing you know he will be having discussions with God.

Yecch...

As I have said before and I say again, energy expenditure has many variables. A calorie does not exist in a vacuum.

My example is that water will boil at different temperatures under different atmospheric pressures, hence the net energy needed to boil the water will be different.

Two people of the same height may have completely different metabolic structures, energy levels, activity levels, genetic predispositions, skeletal structures, sex, hormones... the list goes on and on.... and thus will have different caloric threshholds, even the one for starvation.

To live well, each person has to find his own sense of balance, and I don't think that suffering is essential to growth, although a lot of Dark Age thinkers might have you think so.

Well, he IS a physicist and it works for him, sooooo...it MUST be the long searched for answer that the world has been waiting for. You gotta love pencilnecks.

Well, heck, I lost weight on a diet of my own invention...one hamburger a day and I swam for an hour.
It's after the diet that's the problem.

I know what you mean by a diet of your own making! Here are my diet faux pas... nobody should ever do this...

Age 6 -14 - always a stocky girl, my mother refused to buy me regular jeans because she figured they would not fit right. Wore godawful polyester stretch pants, or jeans with elastic that made my butt look like a bubble. My favorite foods? PASTA PASTA PASTA, white bread, cakes and cookies. Although I did eat eggs, cheese and nuts regularly. I was an active kid who did bike riding, badminton, swimming, and chasing around the neighborhood, but I was a slow runner and never was able to do the Presidential Physical Fitness challenges. My mother was heavy and she yo-yo dieted on 1200 calories. I read all her little brochures.

Age 14 - 142 lbs - decided to go on a lowfat diet over the summer. Eating 900-1200 calories a day, with 2 hours of tennis lessons and 2 hours of swimming lessons 5 days a week, got down to 112 lbs (36-26-36).

Typical menu:
Breakfast - Twinkie with skim milk.
Lunch - ramen and a fruit smoothie, or a couple of slices of Totino's pizza with some skim milk. OR a bag of potato chips and a container of sour cream and onion dip with no dinner (and tummy growls heading to bed). OR a precious chocolate bar.
Dinner - tuna or mackerel on white bread with a banana and a glass of skim milk.

Age 15 - 17, kept scale watching... went down to 900 calories a day when I wasn't happy with my weight. Had lots of belly growling. Learned to think that it was good.

Age 17 - 125 lbs. Went to college. Discovered one can use a giant salad bowl for breakfast with about 5 different kinds of sugary cereal. Started working at Denny's, piled on the pounds eating french fries, onion rings, fried sandwiches, and grand slams down to the last bite. Got a roommate who liked to eat lots of food. We would get little Caesar's Pizza Pizza and each of us would demolish a small pizza on our own until our tummies were hurting.

Age 19 - 145 lbs. Got married. Put on more weight.

Age 22ish - 185 lbs - went on Optifast. Lost 20 lbs in a few weeks. Then got so sick of the shakes that the smell and taste made me want to barf. Did lowfat after that for 2 years and kept it off. But the weight came on after that.

Age 29 - 208 lbs - went on the "divorce diet". Lost 50 lbs in 3 months basically fasting, sometimes eating nothing but a can of soup per day. Dropped down to 156 lbs, jogging in the morning.

Age 30 - 165 lbs, got pregnant and started gaining weight too fast. Ate lots of Chinese food and White Castles with fries. Got gestational diabetes. Controlled it well, but could not eat bagels because they made the blood sugar shoot up. Took insulin shots. Had a healthy baby. Ending weight 185 lbs.

Age 33 - 198 lbs, got pregnant, but watched the weight and only gained about 14 lbs. Did not have gestational diabetes. Ending weight 185 lbs.

Age 33 - 203 lbs, took Chitosan and Metabolife. Stopped the Chitosan because I was feeling symptoms of vitamin D deficiency. Stopped the Metabolife because it was making me jittery and giving me a rapid heartbeat and blood pressure. Did low fat for almost 2 years. Got down to 173 lbs.

Age 35-36 - got totally tired of lowfat and told it to go to hell. Got up to 198.5 lbs. Triglycerides = 700. Went on Gemfibrozil. Got depressed, got GERD so bad, I had to have surgery for the strictures in my esophagus because food was sticking there. Had 3 different painkillers in the medicine cabinet because every morning was painful waking up. My knees started burning when I sat down. Doctor told me it was arthritis and I was just in that aging range.

Age 36 - started Atkins. Energy up, mood up, weight down, pain gone. I really hope I can keep up with controlled carbohydrate eating for a lifetime, because I don't think my body could put up with any more dieting. (38 - 30 - 37). I've still got a ways to go to get firmed up, but boy do I feel so much better... and perhaps understand what I did wrong all those years ago.

I think attempting to lose weight by reducing calorie is a big mistake.

Our bodies don't look at fat as a sign of sickness. Our bodies look at fat as a precious energy reserve which one day will save our lives when food becomes scarce.

Our bodies are regulated. This means that if your weight is 150 lbs, there is data stored somewhere in your brain which says that your weight must be 150 lbs. If for any reason your weight went up or down, your body will always return your weight back to 150lbs.

Additionally, our bodies are self learning. This means that the data which sets our weight amount can also be changed. If your body discovers at any time that you may face a food shortage period which requires more than the body fat set for you, it will change that setting.

Now let us assume that you didn't like your weight and decided to eat less until your weight becomes 130 lb. During the diet you will be saying "I'll suffer for a while until I lose my excess fat so I become fit and healthy!". Your body will be saying "My God! Here is my first food shortage. I'll do my best to use my energy reserve wisely to stay alive hoping that the food shortage will be over before all my reserve is gone!".

At the end of your diet, you'll be saying "Now I'm fit. From now on, I'll be eating enough food to get all the energy I need but not enough to gain any fat back. This way I can live happy and healthy forever!" Your body will be saying "The food shortage is over. Thanks to my energy reserve I could survive this one, however the next food shortag may not be as easy. From now on, I should waste no time rebuilding my energy reserve back and some more so that I can survive the next hader one!"

After doing some research, you'll be saying "My body requires 1800 calories a day to get all the energy it needs, so I'll always make sure to eat no more than this amount." Your body will also do some research and say "I need to replace the lost 20 lbs with 30 lbs. So, if I get 1800 calories a day, I'll use 1300 of them for energy which is the minimum I can live with and use the remaining 500 to make body fat with. This way I can reach my goal in about 30 weeks."

You start eating 1800 calories of food a day, but then discover that you are not full. You feel hungry and dizzy. You resist for a while, but then you surrender and eat as much as it takes to stop your hunger and diziness. At the end, your body reachs its goal and your weight reachs 160 lbs.

You feel bad and forget about dieting. Your body sees no reason to change your weight, so it keeps your weight steadily at 160 lbs and things stay the same for sometime.

One day you wake up and say "I'm not going to surrender. I'm going to start a longer diet to lose 30lbs this time and will never gain them back!" You repeat what you did and unfortunately each time you do it, you end gaining more.

This is the typical trap most obese people fall in. This is what keeps the nation's obesity rate growing year after year. Also, this is the endless game which makes some companies big money endlessly.


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Ummm...a pound of fat equals 3,500 calories. The esteemed physicist is off by 1,000 calories.




Where he gets this little tidbit, I'm not sure. AFAIK, fat is burned by your cells for energy; it doesn't just "evaporate" off your body. One of the byproducts of cell respiration is carbon dioxide, but water vapor??? You lose water vapor through breathing whether you are dieting or not.

It seems our dear physicist is still taking a very Puritan attitude towards weight loss. One that says, you can't achieve weight loss without some form of suffereing and deprivation and that those things are good...almost a form of penitance for having been such gluttonous pigs to get overweight in the first place.

The first law of thermodynamics refers to closed systems. The body is hardly a closed system, IMHO!

Samuel, your entire post is very interesting. Would you please expand into how you think our bodies adapt to Adkins and LCing?

I'd also be interested in this adaptation theory. As far as I know, the body only responds with lowering metabolic rate when daily caloric intake drops below that which is needed to sustain BMR on a consistant basis, which the author above seems to have done if he was truly only taking in 1,350 calories per day and is a 6' 1" male. If I remember correctly, Dr. Atkins suggested for those that were intent on counting calories that 1,800 was a reasonable amount to lose on for most women and 2,000 calories per day for most men. Note this is to lose weight, not maintain it. Obviously, some folks will be able to eat more and lose and some will have to eat less. Being perimenopausal and having PCOS and diabetes, I've found that I need to stick around 1,500 calories per day max if I want to lose. Add to that the fact that he is approaching 60 years old, which means that his metabolism is already slowing, and he may find that over the next couple of decades that he needs to eat less and less to maintain that 175 pounds and "floating" feeling that he's so fond of.
While this may seem attractive to him, it certainly doesn't to me. Realistically, I understand that as we age, our metabolisms slow and we will need to consume less calories per day to maintain a certain body weight, but I really hope I'm never in a position of having to starve myself to maintain. How depressing.
I also don't know if I can agree that we are forever doomed to regain any weight we lose because we lost it through calorie reduction, which if we're completely honest is the only way to cause our bodies to shed fat...give it less calories than it needs for BMR PLUS daily activities, but never drop below BMR. Granted, with low carb most find that they can consume more calories than they did with low fat/high carb and lose weight better (and without being constantly hungry), but even with low carb if you eat more than you burn you will gain weight or at least fail to lose. Low carb also gives you the advantage of switching your body over to using primarly fat for fuel instead of glucose, so your body is more likely to turn to its fat stores for energy than it would if glucose supply was sufficient. The question becomes, how much more energy are you expending using fat for your primary energy source than you were using primarily glucose as that is what I believe to be the heart of the metabolic advantage that Dr. Atkins spoke of?

Oh...and that "butter on the bacon" comment was totally misinformed, but given the rest of the article it doesn't really surprise me too much that he would make such a comment.

"butter on bacon" LMAO

That one cracked me up, but on the whole, I didn't find the article incredulous. All of his assertions were reasonable given the scenario where one wishes to lose weight, whatever the cost of enduring that said loss.

In my view, there can be no question that ANYONE will lose weight if he/she reduces calorie intake by 650. I do agree that most of us can function easily and be fully satiated at 2000 calories per day; and, per the Pysicist's assumption, reducing it to 1350/day is certainly possible especially if one doesn't increase physical activity, which was his premise--to lose weight without excercising.

The hunger which exists is also manageable, but I do agree with his assessment that some of can manage it, while other's prefer not to. Once again, not that I agree with his methodology here, but I do see the logic in his method. There is little to refute the rationality and effectiveness of this approach, given one can adhere to it dealing with the hunger "itch" as he calls it.

My only point is that on a LC diet, in my view, there is a metabolic advantage, however slight. From my experience (and this is in no way scientific) 1350 normal calories will be equivalent to about 1850 LC calories--meaning, with lower carb intake, eating 1850 calories will have the same effect on weight loss as eating 1350 high or moderate carb calories. The big difference is that of course with 1850 LC calories, there is no hunger sensation attached with it; not to mention the added energy level is conducive to more vigorous physical activity should one decide on say a morning run.

So, in my view, the premise is not so different from the weight loss plans we've adopted here in the LC world of eating. The one attribute (perhaps the greatest) is the slight metabolic advantage which allows us to eat more while creating in essence the same energy deficit. Now, I'm not sure how this all fits in with the first law of Thermodynamics, but all I know is that not only does eating LC works, but easily accords me enough energy to stick to my workout regimens as well.

Regards,

Frederick

Thanks for appreciating my post. I can tell for sure that high carb, low calorie dieting could only make things worse. This should automatically mean that our only hope is in low carb dieting.

Now here is why I think low carb dieting could do better:

For millions of years some humans have been living in areas where the food available was mostly vegetables and some other humans have been living in areas where they could only hunt to get their food. The first type has been eating similarly to cows and pegs now. The second type has been eating similarly to lions and tigers now.

For the first type, food has been seasonal. So their bodies have developed a mechanism to store energy during the season when food is available and use it during the season when food is scarce. For the second type, food has been available mostly year round, so their need to store energy has been less. Additionally, the second type needed to be lighter and to have more muscles to improve their ability to hunt.

When you are on a high carb, low calorie diet, you are telling your body that you are a human of the first type who is currently in his food shortage season. So your body will use its energy reseve and at the same time will believe more in the value of its energy reseve. When the diet is over, it must make you equal amount of body fat or more. In no way it could believe that your body fat is no longer necessary.

When you are on a low carb diet, you are telling your body that you have moved to a different environment. Your food is no longer seasonal and you need to be light and have more muscles to fit your new environment.

Finally, these are just my thoughts. Low carb dieting is new to me and nothing I know is guaranteed to be correct. Thanks again.

what's wrong with butter on my bacon?

"Moreover—and this may sound silly coming from a physicist—I was surprised that I began to feel lighter. I no longer walk down streets—I float."

What's this guy been smoking/sniffing/ingesting?

shortstuff

(Sorry, sometimes I just can't help myself.)

... it's the kind of euphoria that ascetics might ascribe to. It's hunger to the nth degree. Maybe even blood pressure that went a little south or a lack of nutrients. Floating is certainly not a "normal" state of mind.

I'm sure that the recent exploits of the magician in London who locked himself up in a little box with no food for 40 days, I think it was, probably gave him this same euphoria.