When it comes to calories, inefficiency is the name of the game.
We know that less weight is healthier and leads to longer life, but the desire to eat runs deep, and dieting through willpower works for almost no one. So we look for tricks that will let us eat more and weigh less. Two articles from Scientific American this month are most enlightening. One demonstrates that the number of calories we extract from food varies widely from the standard method as reported on the label. The other recounts ways in which some foods triggers hormonal signals that say “burn me!” while others tell the body to “store me as fat!”
There exist a handful of people who can keep weight off through willpower alone, but they are vanishingly rare. A study I like to cite reports the weight change after three years of people who restrict food with guidance, support and medical supervision. The bottom line is that the average dieter gains weight. Here’s a review article called Diets are Not the Answer.
Measuring food energy
A calorie is a measure of the chemical energy content of food. In the 19th century, the first, crude theory posited that what the body does with food is equivalent to burning it in oxygen. The first methodology for determining the calorie content of food was simply to burn it in a chamber surrounded by a water jacket, and measure the increase in temperature of the water. Amazingly, this crude measure became standard and has gone unquestioned for 120 years. An article by biologist Rob Dunn of North Carolina State University questions this practice in a challenge that is long overdue.
Usually, we think of efficiency as a good thing. But the efficiency with which we use food affects how much fat we store from a given number of calories. If we want to eat more and weigh less, efficiency weighs against us. For every calorie we put into our stomachs, we get some fraction of a calorie out as food energy, and that fraction can vary widely with the type of food, how well we chew, whether the food is cooked, and the particular mix of bacteria in our guts.
Factors affecting our digestion efficiency
Fruit, tubers, and flour are easily digested and calories are readily available.
Nuts and seeds are often rich in fat, so they register as high-calorie foods. But they are harder to digest, and the body gets less from them. Seeds that are unchewed go right through us. In fact, many plants use animals to help disperse their seeds, and evolution has designed the seeds to survive digestion. Most nuts are partially chewed, and some small pieces pass through undigested. There is a big difference in available energy from eating peanuts and peanut butter, though the labels will list the identical calorie content.
The body needs to expend energy in digestion, and this can take a substantial bite out of the available food energy. Cooking breaks down the cell walls in meats and vegetables, and they are digested more thoroughly and with less energy expenditure. If you’ve ever tried a raw food diet, it’s very hard to gain weight, no matter how much you eat.
Food fiber is not digestible by the bacteria that inhabit human stomachs, so its calorie content contributes negligibly to what we actually absorb. Even better, a high-fiber diet reduces the time that food spends in the intestine. A rapid transit time is healthier in terms of the quantity and the quality of the extracted nutrition.
Transit time varies with the calorie density of your food, as well as the fiber content of the diet. Vegetarians have shorter transit times than carnivores, simply because there is more volume for the same calorie content. A typical American diet of meat and starch leads to a transit time of 3 days. By eating lots of greens, drinking extra water, and supplementing with raw wheat bran (an acquired taste, to be sure, but it costs practically nothing in bulk), you can get your time down to 18 or even 12 hours. It could make a big difference in your weight.
Measure your transit time by eating beets with a meal, and noting when your stool shows red.
The last factor is the mix of your intestinal flora. Some bacteria do such a good job of digesting your food that they take most of the calories for themselves, leaving little for you. Others are more generous. (Remember, inefficiency is the name of the game.) It is known that people show a lot of variability in the kinds of bacteria that inhabit their guts, but the science of how to manage your unique microbiome is in its infancy. Here is a New York Times Magazine article by Michael Pollan from last May.
When it comes to calories, we’d prefer that the food we eat go right through us without being absorbed. But for supplements, herbs, medications, and vitamins we want maximal assimilation. Best to take supplements at a different time of day from high-fiber meals. Some can be absorbed well in a fasting stomach. Other supplements are absorbed better with food, and some go better with a meal that includes fats. A light, low-fiber meal leads to better absorption than a fiber-rich meal.
Carbohydrates vs Fats
Another article in this month’s Food Issue of Scientific American explores a theme that has been the theme song of Gary Taubes for fifteen years now. His thesis is simply that eating carbohydrates signals the insulin metabolism to store fat, while eating the same calorie content as fat or protein, the calories are more likely to be burned. I think he’s right.
Taubes is far from the first to present this idea to the public. Robert Atkins said the same thing to the last generation. Barry Sears tried to lead us through the biochemistry in his Zone books. I’m old enough to remember Calories Don’t Count, by Herman Taller, which launched my mother on a low-carb diet in 1961.
Taubes builds his case on the fact that during the same time period when American and European consumers were being sold a lower fat diet (beginning about 1980), the obesity epidemic was born. I’m usually dubious of cross-cultural epidemiology because there are so many potential confounding factors active at the same time. But in this case, Taubes’s case is built on sound physiology as well. Carbohydrates require minimal digestion, and appear in the blood stream instantly as glucose. Insulin is secreted to moderate glucose in the blood, and signals the body to remove the glucose and store it as fat.
Taubes is a journalist, not a scientist. I have to read between the lines to fill in the science. But the advantage of his investigative approach is that he tells some of the political backstory about how commercial food interests have derailed government scientific investigations, distorting the results that are reported to the public. Taubes details the experimental design of a study which he has initiated that might eventually resolve the split in the nutritional community over low-fat vs low-carb diets.
It was just a few years ago when “high-fructose corn syrup” was considered to be an attractive ingredient to list on a label, because “sugar” makes us think of an unnatural, refined product, while “fructose” derives its name from being the predominant sugar in (natural) fruits. Now fructose has been singled out as the worst carbohydrate, with the most direct and immediate effect on the signaling that moves the body toward obesity. A 2011 British study drills down to the biochemistry of AMP and ATP. When the mitochondria burn sugar to deliver usable energy to the cell, their deliverable product is ATP. When the cell deploys the energy, ATP is returned to its low-energy form, AMP, and recycled. Glucose or sucrose are two common dietary sugars, and they increase the amount of available ATP, which signals the body to stop eating and use the available energy. But paradoxically fructose triggers the opposite signal, depressing ATP and stimulating the appetite for yet more food, while storing the energy as fat. It is this mechanism that makes fructose more dangerous to health than other carbohydrates.
Adding fuel to the fire, fat cells themselves are a source of insulin and its inflammatory cousin IGF-1. Circulating insulin and IGF-1 close the feedback loop that keep the body’s metabolism in an obese mode. A side-effect is elevated risk of cancer.
Low-protein vs Low-carb diets
There are two schools of thought on the broad basis of a pro-longevity diet. The first seeks to restrict protein, because in lab studies, protein-restricted animals show increased life span even if calories are not restricted, and because IGF-1 is lower in protein-restricted humans. The second seeks to restrict carbohydrates (and fructose especially) based on the above analysis of the insulin metabolism. For the last 12 years, I have pursued a low-carb, high-fiber vegetarian diet coupled with intense exercise, and it works well for me. I don’t eat grains or potatoes, but I do eat a good deal of fruit. I don’t know if fruit is simply my personal weakness, or if it helps me to keep up the energy for a very active life style.
I know others who have had success with the low-protein approach.
Theoretically, it is possible to combine the two approaches with a diet that is overbalanced toward fats and fiber. Are you old enough to remember Frances Moore Lappé’s campaign to get us to eat complete protein by combining the 8 essential amino acids? Well, now it turns out that incomplete protein (from vegetable sources like lentils and almonds) helps to keep the body in its protein-deprived state, promoting both health and longevity. (To her credit, Lappé changed her recommendation about complete protein many years ago, as the new science became available.) A diet that restricts both carbs and protein (think avocado salads with olives and walnuts) seems extreme, and I have not seen any studies. Perhaps it is the next cutting edge, or it may just make you feel crummy.
Excellent article, as always. I may use some of it and translate it for my blog (which deals a a lot about nutrition and exercise), it you don’t have any problem with it ?
I would never have thought that the transit time was 3 days … I need to do the beet experiment.
First thank you for another great article with lots of side information to look into :-). I am highly intrigued by the caption of the image – 5 feet is quite a bit.
But regarding Taubes book I want to shoot a warning here. Especially in his book and other articles/interviews he always goes on and off about how the release of insuline through sugar is the thing that makes us fat.
I was trying out his theories and just ate meat (read bacon, pork chop, grilled chicken) for a couple of weeks – and gained a horrible amount of weight. The one thing Taubes just “forgets to mention” is that the body can store fat too. So if you eat 4000 calories of bacon (which equals to a modest package of 800 grams or so which in turn is only something like 400-600g after cooking) you will gain weight. I found it quite easy to overeat on the calories when eating high fat/protein partially because there was so little volume (and maybe so little nutrients in terms of vitamins…?) in the stuff.
Also I found it to be very hard to count calories of meat products. Information how many calories say 100g pork chop have is hard to come by and varies wildly by how you prepare and how fatty the meat is.
On the other hand I have been on a fruitarian (read only fruits and fruit-vegetables ala cucumber/tomato) diet for both months and weeks and found not only that I would have wild amounts of energy, be quite healthy, lose weight but also maybe most importantly come by with way less calories (about 1500 calories at 178cm and 70kg) without restricting how much I eat.
Cucumbers are kinda great because you can constantly eat for two or three hours and then realize that you most likely lost more calories from chewing than you got from the green thing ;-).
I also found “Never Be Sick Again” by Raymond Francis very intriguing. While clearly his book lacks the scientific standard of a Josh Mitteldorf blogpost 😉 and he cites many things that are either completely false or could be disputed his underlying message is intriguing:
Eat for nutrition not for calories (and avoid toxins).
At the end of the day no food you eat is truly bad for your body: A calorie burned in a mitochondria doesn’t care if it’s a tomato calorie or a beef calorie. On the other hand the more nutrients you eat the easier is it to avoid eating lots of calories (most nutrient dense foods are equally dense in fiber and have few calories plus a high water content).
And if you take a close look at all the popular diets out there all of them have certain problems associated with nutrient lack. For example pure raw foodists who eat no animal products whatsoever and very low fat in general from nuts and avocados will start to have small wounds and splitting off skin at their finger tips and also a feeling of nervous restlessness. Both can easily be cured by a small addition of cooked food and salt in the diet (as would be considered non-raw).
I think that it’s most important to see that your body does not lack any important nutrients (say vitamins and minerals) because what good is a caloric reduction if you become sickly all the time because your immune system does not have adequate amounts of vitamin c to fight the nasty evils under your skin?
There is also at least one study who explores the relationship between intake of essential nutrients and appetite. Their conclusion was that lack of essential nutrients increases your appetite. Sorry for not being able to cite the study correctly but I have no idea where I found it in the first place :-(.
Nevertheless I think you deserve a medal of honor for the most superhuman feat to eat that much bran every day.
By the way is Suicide Genes out already? My blog is soon going live and I would love to do a review of your book.
Thanks for your kind words, and for the abundant supplementary information you’ve provided. And thanks especially for the warning about meat-based low-carb diets. I have been a vegetarian for 40 years, and have no experience with carnivorous diets. Perhaps one reason that low-carb works so well for me is that there are no truly carb-free vegetarian sources of protein, so there’s built-in moderation to my carbohydrate restriction. I am very comfortable with vegetarianism, both because I recoil at killing animals, and because there is data to suggest that vegetarian is pro-longevity.
You say that Gary Taubes is not a scientist (true). But he’s no ordinary journalist, and to say he’s not a scientist strikes an overly dismissive tone. Taubes has an undergraduate degree in applied physics from Harvard, and a M.S. in aerospace engineering from Stanford. That scientific training has served him (and his readers) quite well.
I have nothing but respect for Taubes. He sees some things about the biology of obesity that the experts have missed for years, and he is one of the most effective advocates in the field, precisely because he has the connections and the skills of a science writer.
Something to think about:
Albert Einstein was no scientist when he published the theory of general relativity. Nicola Tesla never graduated college.
If you could choose to make a great invention or be a scientist, what would you choose?
I don’t know Taubes but sometimes people even deliberately choose not to be scientists to be more free in the pursuit of their passions.
In Science Magazine this week, an experiment is described in which transfer of bacteria from the intestine of a lean mouse to an obese mouse induced weight loss. For the “lean bacteria” to take over required a change in diet.
Hey Josh — I love your name. 😉 Anyways, I’ve been reading your (great) blog for a couple of weeks now, and when I got to this entry, a question occurred to me. I understand that a low-protein diet is considered one way to increase longevity. However, I also understand that loss of muscle mass/strength in seniors is a huge cause of mortality, as it leads to weakness/difficulty moving/falls, and things can spiral from there. Increased protein consumption is one of the best ways (along with resistance training) to maintain muscle and strength. So — how to reconcile this? Eat less protein, but lose muscle as the years advance? Or eat more protein to maintain strength, but perhaps shorten lifespan via other mechanisms?
Hi, Josh –
I’m with you. I don’t think that protein restriction is an attractive life extension strategy – more of a lab curiosity. The levels of protein have to be very low before it works, and as you say there is a price to pay. So I favor a low-carb, low-glycemic-load diet, with the caveat that people are different and everyone must explore for himself what feels good and he can stick to.
Thanks for the reply. I’d also be curious to know your take on caloric restriction vs. intermittent fasting. My feeling is that intermittent fasting is an easier way of achieving most of the benefits of CR, and also makes it easier to maintain muscle mass. However, you would probably know more about it than I. If you’ve already written about this somewhere, I’d be interested in reading that post(s).