1. ## Measuring calories

IIRC when they determine how many calories (which are actually kilocalories) are in, say a chocolate sundae, they basically just burn it and see how much energy is produced.
Is this a good way to measure this? Is digestion thermodynamically the same as combustion?

2. Originally Posted by Tom Mazanec
IIRC when they determine how many calories (which are actually kilocalories) are in, say a chocolate sundae, they basically just burn it and see how much energy is produced.
Is this a good way to measure this? Is digestion thermodynamically the same as combustion?
Pretty much. As Lavoisier said, "La respiration est donc une combustion."
Carbohydrates and fats are completely oxidized during normal metabolism, so the bomb calorimeter gives an accurate result, barring a slight correction for the fact we don't absorb all the nutrients we ingest.
But there's an overestimate for proteins, which aren't completely oxidized in the body during normal metabolism--in other words, you excrete some combustible protein metabolites. So if you run bomb calorimetry on the nitrogenous waste the body excretes, you can subtract that from the bomb calorimetry of protein, and come up with the actual metabolic calorific value of protein.

In practice, no-one puts a chocolate sundae into a bomb calorimeter these days, however. The food is analysed for its fat, carbohydrate and protein content, and the calorific value derived using well-established conversion constants.

BTW: You can't say "calories (which are actually kilocalories)". The unit "calorie" is always a calorie. A "Calorie" is a kilocalorie.

Grant Hutchison

3. To add to what Grant said, It is also that not all Calories are the same in digestion. Proteins are used as amino acids and then only burned at 4 Cal/g , like carbs, if carbs and fats are not available. Carbs are used to make glucose so do get burned. If you eschew carbs, so called keto diets because of the alternative metabolism, ketosis, you burn fats at 9 Cal/g approx. and also excrete fats as ketones. Excess glucose can also be converted to fat as part of the tight glucose control by insulin, (insulin tolerance is the condition called type two diabetes). So consuming and using Calories is more complex in digestion than in combustion. Alcohol is yet another metabolic

4. As long as we are discussing Calories, how many Calories do I have to take out of my eating to lose a pound?

5. Originally Posted by Tom Mazanec
As long as we are discussing Calories, how many Calories do I have to take out of my eating to lose a pound?
When I was a student, I was taught that 3500 Calories equals one pound of body fat. That's probably true enough for the first few pounds you lose, but thereafter your physiology will flip into "starvation mode", and start to work against you by conserving energy. This is why dieters often hit a wall after initially promising weight loss. At the extreme, people can get into a mode in which any further weight loss requires them to eat so few Calories that they start to become deficient in micronutrients.
When I worked with the obesity surgery team, morbidly obese people would receive dietary supplements, supervised by specialist dieticians and physicians, to help them drive their weight down into the window that allowed me to anaesthetize them safely for their proposed surgery.

Grant Hutchison

6. Originally Posted by Tom Mazanec
As long as we are discussing Calories, how many Calories do I have to take out of my eating to lose a pound?
I have diabetes and have been struggling with that myself. As near as I can tell, it's virtually impossible to eat the same amount of calories per day. Too many vagaries in actual prep and cooking. It strikes me that more activity is preferable to less calories, if you are already consuming a relatively balanced diet.

I managed to cut my A1C by more than half in a year. (13.9 vs. 6.5). I also lost 33 lbs. in the same time period. Unfortunately, I have to do the whole thing all over again because my cholesterol is spiking. That's one of the dangers of making choices when you don't know much about diet and nutrition. So, now I have to figure out how to knock off all of the unhealthy (for me) stuff that is driving up the cholesterol. And it's not real clear to me what that would be. So, I won't be writing a miracle diet book any time soon.

It's all a delicate balance. People (my wife a nurse, included) freak out when they seem my meal logs. I tend to plan for 1400 calories per day at meal times. That too little. I also have 5 different kinds of preplanned snacks, each is about 120 calories and a sixth that is about 30 calories of just veggies. Sometimes, I eat all five and two at once. Other days, I eat none of them. It really depends on what my blood sugar is doing and how I feel, but obviously that isn't a valid measure if I have a cholesterol problem. I've reached a plateau where I can't get my insulin down, but also can't loose any more weight through diet alone. Some days, I am real stable but entirely drained. Other days, I feel great but the numbers are all over the place.

I drive my low carb friends nuts because if I plan ahead, I can actually eat a good amount of carbs if I feel like it. They don't get the idea that the cost of doing so is either move more or faster or increase my insulin. I don't eat a plate of carbs that often, because I view the insulin as a necessary but dangerous crutch. I can arbitrarily spin up my dose to get "rid of" carbs (well... gain weight). One of my fears is following a friend who was cranking up the insulin to drink beer without moderation. He lost a leg before the end, but he said his numbers looked great until he reached a certain tipping point. Having very high or low blood sugar can really damage your ability to make choices, so I don't doubt he was accurately reporting at first. It was a slow creep upwards and poor diet over a couple of years (like just two) that got him.

As Grant says, I wonder how bad his nutrients were. He could have had multiple deficiencies that when added to diabetes were horrible. I try to avoid that with good foods, but I still need vitamins because there are just certain things I won't eat because I won't be able to stop. Orange juice is my kryptonite. I love the stuff, I can't touch a drop of it. I've found that it's true that you can drink orange juice to remedy low blood sugar, but I feel lousy for the rest of the day. I probably need vitamin D too, but I don't like milk so I have to find other sources or pop a vitamin. I don't like taking pills, but I do it.

It's all a balance.

7. The evidence, peer reviewed, that losing weight is best achieved by restricting carbohydrates has been published since the 50s and expanded by excellent controlled studies. Most studies do concentrate on obesity so it is important to distinguish any normal weight diet from deliberate weight loss. I feel the name type two diabetes is a bad name, it would be better to call it insulin tolerance. The difference between not making insulin and becoming tolerant, ie not transferring energy to cells via insulin, is chalk and cheese. Our bodies have at least three metabolic abilities to make energy from food; glucose from carbs or proteins, ketones from fats and aldehydes from ethanol. We also lay down fat using insulin to convert glucose. So , if overweight, you can still eat loads of Calories if they are all fat! Not an easy diet! But as soon as your liver converts to ketosis, the fat is consumed. It has been shown to beat starvation which causes protein loss.

8. Perhaps the most convincing paper is from Young et al., Cornell univ., 1971.
Young worked with obese men using carefully controlled 1800 Cal. Diets containing 30, 60 or 104 grams of carbs.
The weight loss in pounds per week was:
At 104 g carbs, 2 lb/ week,
At 60 g, 2.5 lb / week,
At 30 g, 3.73 lb per week. (This is higher than the theoretical fat loss through metabolism.)
Fat is shed as Kekwick and Pawan found in 1956.

9. For Calorie nerds, the earliest reference I have found was published in the Journal Metabolism, 1957, journal 6 issue 5 pp 447 to 460.
Kekwick and Pawan made obese men eat 1000 Calorie diets of four types. 90% carbs, 90% protein, 90% fat and a mixed “normal” control.
On the control diet they lost between 100and 200 grams per day, as you would expect on 1000 Calories.
On the protein diet they lost up to 500 grams per day and excreted nitrogen.
On carbs they lost from 100 to a gain of 100, net zero change, over a couple of weeks!
On fats they lost from 350 to 650 grams per day. By far the most weight loss regime.

This basic metabolism science has largely been ignored by public policy while obesity has got steadily worse as food producers replaced fats with complex sugars, (they are just digested as carbs) .

The various studies have shown how to reduce weight but the corollary of inducing weight gain has ethical issues although in my opinion it is obvious. Eating carbs to excess is a really bad idea for individual or public health. It is not just a Calorie count.

10. Grant (or anyone, but I expect it will be Grant), what is the disadvantage of “starvation mode”? I expect there is a disadvantage or we would be in this more efficient mode all the time.

11. Well I am not Grant but starvation is of course part of our not so distant ancestry and it seems when starving we conserve fat reserves by also burning up muscle. It does not compare well to eating if the goal is to reduce excess fat. You can live on protein but most carb free protein comes with fat too. Meat, fish, cheese. I tried starvation , for 28 days, as an experiment although I took vitamins and extra water. It does have psychological highs so it is easy to see why some people practice starvation, although the metabolic changes do not happen for a few days, we use up stored glucose for at least two days before ketosis begins. Living on low carbs, say, less than 100 or even 200 grams per day, is an easy habit and has, as far as I can see, no adverse effects. Starvation is not good for more than a week of self denial. If using it to lose weight, I find you must give up ethanol too. Not only a rich Calorie
Source but it messes with metabolism too.

12. The disadvantage to starvation mode is that it limits your ability to regulate body temperature and to exercise. It's a last-ditch effort to survive lean times by shutting down functions that otherwise improve survival.

Grant Hutchison

13. And while we are talking about food restrictions does that really double lifespan? Could whatever effect this does in animals be “normal” for humans, perhaps so we have grandparents to help us raise children? I mean with all the famines and monks in history you would think it would have happened by now.

14. Calorie-restriction diets of the kind that show longevity results in animals are not equivalent to famines, and I don't understand the relevance of monks, or what you feel "would have happened by now".
These diets are a way of staying permanently in starvation-mode physiology without developing micronutrient deficiency, which is difficult to do. So, no, humans do not normally exist in that state, and could not successfully exist in that state until quite recently.

There a decent, recent plain-language review of the thinking behind calorie-restriction diets here.

Grant Hutchison

15. I was thinking of the fasts Christian and Buddhist monks practice.

16. Fasting for part or even all of a 24 hour period does not switch us to ketosis, we store glucose, but there has been evidence of improved health and or weight loss from , for example , regular 16 hour fasts as a habit. That does not seem surprising given a hunter gatherer past. Longer fasts take you into the ketosis switch, at two to three days which can feel like a hangover. Thus a high incentive to eat, but after that there is a euphoric phase of fasting when metabolising fats. That may well be why some people include long fasts in religious practices.

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Originally Posted by Tom Mazanec
IIRC when they determine how many calories (which are actually kilocalories) are in, say a chocolate sundae, they basically just burn it and see how much energy is produced.
Is this a good way to measure this? Is digestion thermodynamically the same as combustion?
It is not precisely the same process, of course, but we are not interested in the process itself, we are interested in how much the "energy content" of the involved substances changes during the process (the general term "energy content" could be made more specific, but since this is not a thermodynamics lecture...).

The energy content is a state variable, that is, it only depends on the thermodynamic state of the substance and not on how this state has been reached (in other words: it does not depend on the process which led to the current state). The question "How much energy is liberated by the oxidation process which occurs during digestion?" is really the question "What is the energy difference between the original unoxidised substances and the final oxidised substances?".

The answer only depends on the energy content of the unoxidised substances, compared to the energy content of the oxidised substances. The answer is independent of the details of the process which leads from the initial state to the final state. To measure the difference you can therefore use any process which leads from the same initial state to the same final state. You could use the digestion process itself, you could use any arbitrarily complex process involving horrendously complicated chemical reactions (maybe even introducing non-food substances as long as they are removed again later in the process), or you can use simple burning. You only have to make sure that the initial and the final states are the same as in digestion.

Regards,
Thomas

18. That is an excellent answer leaving the key element of what digestion actually does. Some food is used as proteins , some is burned , some is laid down as fat and some is eliminated, and the ratios change with circumstances. So the Calorimeter value is not necessarily the same as the digestion value but can sometimes be close. There is also the question of the water energy value but maybe that is a different question.

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