This was a frustrating post to write.
Not because I couldn’t decide on the words to write, but rather it seemed to me that the scientific community couldn’t decide on how our food choices makes us fat.
Sifting through the literature, I found out quickly that the science is even more complicated than I expected. There are no tidy explanations accompanied with definitive graphs and figures, just possible explanations tempered by “we need more research.”
You see nutritional science is a fairly new and imprecise field, and most studies that come out are just small drops in different buckets.
To create meaningful recommendations from the knowledge, there needs to be lots of drops in one bucket or another, which takes a lot of time and a lot of money (which itself creates lots of problems). Compound that with the fact that we are all biologically different and you can see why it’s difficult to write a definitive post, let alone find a single optimal way of eating based on human biology.
So instead of diving deep into the actual mechanisms at play (though I’ll mention a few here and defer to experts for the explanation) I feel the best thing to do is to curate the current conclusions around two questions that get the lion share of the confusion when it comes how we get fat:
Calories still matter
According to Dr. Jules Hirsch, Obesity Researcher and Chief Physician of Rockefeller University:
“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.”
So if a calorie is a calorie then all I have to do is eat less to lose weight, calories in calories out right?
Yes this is true, if you eat less calories than you normally do, no matter what type of food you eat, you will lose weight, that’s a fact, but there are a few things that affect how the body processes calories.
From a biological standpoint a calorie is a calorie, it’s just a measure of the energy derived from a food source, with protein having 4 calories per gram, carbohydrates 4, and fat 9. Humans also, as Dr. Hirsch describes above, are subject to the first law of thermodynamics and therefore the ultimate arbiter of whether you store fat or keep it off is the amount of calories you ultimately ingest vs. what you burn at rest and during activity.
The biological descriptor couldn’t be any simpler, but in the real world it isn’t always this tidy.
For example, calories in fiber aren’t digested fully or not at all, “With a very high-fiber diet, say 60 grams a day, you might lose as much as 20 percent of the calories you consume,” says Wanda Howell, Ph.D., a professor of nutritional sciences at the University of Arizona. Form also seems to matter, with liquid calories (especially those from soft drinks and juice) being highly nefarious in comparison to whole foods, because liquids, like soda, do nothing to make you feel fuller and often are added calories.
So a calorie isn’t necessarily always a calorie, so why the confusion?
According to Marion Nestle (who we’ve mentioned here on the blog),
“The studies that have measured calorie intake, that have put people on calorie-reduced diets and measured what happened, show no difference in weight loss based on composition of the diet. When people are essentially incarcerated, when all intake is weighed and measured, they will lose weight if the calories in their diets are reduced — regardless of the composition of the diet. That’s why we hear a calorie is a calorie. But no one lives under experimental conditions, and foods are complicated mixtures.”
In addition, Mark Bittmann of the NY Times writes:
“The “calorie is a calorie” argument is widely used by the processed food industry to explain that weight loss isn’t really about what you eat but about how many calories you eat. But if it were just about calories, you could eat only sugar and be fine. In fact, you’d die: sugar lacks essential nutrients.”
The bottom line is this, a calorie isn’t always a calorie in the real world. Fiber and form matter, as well as the environment and conditions we live in. But one thing is certain, calories still count, if you eat more calories than you need, you’ll get fat. As Marion Nestle suggests, it seems to come down to eating less by eating better. But as you’ve seen in the macro food environment and micro food environment it isn’t easy to eat better, since food companies, norms, and our own psychology trick us into eating more than we should.
But what about carbs like rice, bread, and fruit? Carbs make you fat, right? Should I be eating low carb to keep weight off and to lose weight? Is diet composition, in particular carbohydrate quantity, the magic bullet to eating healthy and maintaining a healthy weight? Let’s take a look.
Carbohydrates aren’t the reason you’re fat.
First off it is true that certain demographics respond very well to low carb diets, including those who are obese, sedentary, insulin resistant etc, but that doesn’t mean that everyone needs to eat to low carb to lose weight and be healthier. Let’s look at the carbohydrate hypothesis of fat accumulation to see why some people demonize carbohydrates.
Those who are in the low carb camp often posit that weight gain is caused by the hormone insulin, which in turn makes the amount of carbohydrates you consume the reason you are fat. Instead of writing the whole thing out, here is a video that summarizes the basic process. Alternatively you can check out this infographic.
So by avoiding foods that cause insulin spikes aka eating a low amount of carbohydrates you can avoid putting on fat?
The short answer is no.
The body is much more complicated than the carbohydrate hypothesis lays it out to be, there are many other hormones and processes that affect the regulation of fat in your body, and in fact the literature seems to support the idea that most free living populations keep weight off if they eat carbohydrates. For the long answer I defer to Dr. Stephen Guyenet, obesity researcher and blogger at Whole Health Source, on why the carbohydrate hypothesis of obesity just doesn’t hold up:
“The fact is, insulin spikes after meals temporarily decrease fat release from fat cells, but if you look at total 24 hour energy balance, insulin spikes, in conjunction with all the other hormones that are released in response to food ingestion, do not cause fat accumulation. This is exactly how you would expect the system to work if it were designed to constructively handle a wide variety of macronutrient ratios, which it is. Just as cholesterol did not evolve to give us heart attacks, insulin did not evolve to make us fat. “
Dr. Guyenet goes on to say,
“Another problem with the hypothesis is a thing called the insulinogenic index (II). The II is simply a measure of how much eating a food increases insulin, per unit calorie. It turns out, it doesn’t correspond with the carbohydrate content of the food very well. In particular, protein-rich foods such as beef can increase insulin secretion as much as certain starch foods such as pasta, or more. High-protein diets, as many of you know, aid with weight loss. Some have suggested that this is because of glucagon release by the pancreas in response to protein. That may well play a role, but if we are going to invoke glucagon, then aren’t we acknowledging that other signals besides insulin play an important role in this process? That’s the larger point I’m trying to make here– you can’t just look at insulin, you have to consider amylin, glucagon, GLP-1, ghrelin, leptin, stomach distension, and all of the other short- and long-term signals that are activated in response to nutrient ingestion and changes in body fat mass. These collectively regulate food intake and long-term body fatness via the brain.”
The basic idea is that insulin and therefore carbs aren’t to blame here. The truth is that the science still isn’t sure about how it all works, but it seems that diet composition in terms of macronutrients will have very little (if any at all) measurable effect on your body fatness.
3 things really:
In the next post we’ll tackle another fascinating idea around healthy eating, one that we alluded to in the quote from Dr. Guyenet, the brain’s role in choosing what you may eat, and the food industry’s role in rewiring your brain that make your body “want to be fat.”
Photos via Vox Efx, Neeta Lind
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