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.