Calorie counting is easily one of the most effective ways to lose weight. Flexible dieting (or “IIFYM”) has become one of the biggest nutrition crazes as of late, with fitness influencers posting the macronutrient breakdown of their meals. They weigh their portions and track their intake. While it has been proven that a caloric deficit will ultimately result in improvements in body composition, the story isn't quite so clear cut. In fact, you may be counting your intake and misinterpreting what all of that information means.
A kilocalorie, more commonly referred to as a “calorie,” is the amount of heat that is required to raise the temperature of 1 kilogram of water one degree Celsius. While we still have a lot yet to learn about the science of nutrition and digestion, there are a few ways in which your caloric estimates may be inaccurate.
Calorie labels aren't always accurate.
Your body breaks down all foods differently, depending on their chemical and nutritional profile. For example, researcher Janet Novotny and her colleagues tested the nutritional content of walnuts. She found that we metabolized about 21% less energy than was predicted by the labels. So, a serving of walnuts might say that it is 180 calories, but we are only possibly absorbing about 145 calories. That is a pretty substantial disparity in caloric intake!
Additionally, Gebauer at all tested different types of almonds (whole unroasted, whole roasted, chopped roasted, and almond butter) in equivalent quantities. Surprisingly, the body absorbed the most calories from the almond butter, followed by the whole chopped roasted almonds. Subjects absorbed the least amount of calories from the whole unroasted almonds. It seems as though the roasting process changes the structure of the almond's cells allowing our bodies to digest more of the nut. It appears that if you're looking for the greatest bang for your buck with nuts, the raw variation is far superior to a nut butter. The exact reason for this phenomenon is unknown to date.
Another study done by Carmody et. al. concluded, "...cooking substantially increases the energy gained from meat, leading to elevations in body mass that are not attributable to differences in food intake or activity levels." This means that we are able to absorb more calories from cooked meat than the equivalent amount of raw meat. Here, the cooking process alters the way it is digested and used for energy, in that our bodies can extract more chemicals from cooked food, as they do not have to work as hard to break them down. That is to say that one would expect to consume more calories from a well-done steak than from an equivalent sized medium-rare steak.
Dr. David Bauer notes that "calories are created equal, but their availability from foods is not equal." So what we do with the calories we consume is highly variable based on the processing (or lack thereof) of those foods.
Dietary fiber can influence weight loss.
The USDA recommends that women get about 25 grams of fiber per day, and men get 38 grams per day, yet some estimates report that many people only get 12-18 grams per day. A few studies have guessed that fiber can influence not only our satiety (leading to a decrease in caloric consumption), but also the size of our waists.
A study done by Du et. al. of fiber intake in European citizens over the course of about 7 years found an inverse correlation between cereal fiber intake and waist circumference. This means that individuals who increased cereal fiber consumption had smaller waistlines. There was a less significant effect with fiber from fruits and vegetables.
Again, these changes in body composition may be due to the feeling of satiety that comes from an increase in fiber intake, but that is still poorly understood.
So, if you eat 500 grams of oats, the overall satisfaction is going to be very different than eating 500 grams of chocolate crispy cereal. You may find yourself hungry within an hour after eating the gummy worms, whereas the equivalent amount of oatmeal could keep you full for hours on end. If you're in a caloric deficit, it's ideal to choose foods that will give you the most volume for your calories. Our bodies cannot convert certain types of fiber (insoluble fiber) into energy, and thus, it isn't fully digested and you may not absorb as many calories from it.
Your gut bacteria influences the way you digest food.
Now, the science of the gut microbiome is quite new. There aren't a lot of papers (especially not using human subjects) dissecting the gut's influence on weight gain, but the current body of evidence seems to show clear differences in the microbiome of lean versus obese populations.
Research comparing the gut bacteria in lean and obese twins found that obese individuals had a smaller variety of gut bacteria than did their leaner twins. This discussion becomes one of the "chicken or the egg," in that we do not know if the gut bacteria changes due to fat gain, or if those with a specific type of gut bacteria are more prone to weight gain in the first place. Research over the next few years will dissect this topic more.
One case study of a woman who got a fecal matter transplant from her overweight daughter (yes, that's exactly what it sounds like) demonstrated considerable weight gain after the procedure. These procedures are typically done to eliminate harmful gut bacteria, but the side effect of an increase it fat mass was unexpected. Nearly 16 months after the procedure, the woman gained about 34 pounds. After another year-and-a-half, she gained an additional 7 pounds, despite participating in an exercise program and a liquid protein diet prescribed by a medical professional. She was tested for thyroid dysfunction to no avail. While this is a study of n=1, it lead some researchers to speculate that gut health may have a significant impact on body composition.
For now, researchers believe that some individuals with less diverse microbial communities may be more likely to gain body fat, despite their dietary habits. Some individuals can slash their caloric intake down to a mere 1,200 per day and still hold on to ample amounts of body fat.
In short, even if you’re tracking your calories closely, your estimates may be 15-20% off based on the types of foods you eat and the microbes in your gut. If your weight loss is stalling, there might be more to the story than meets the eye and you may have to tinker around with your diet to yield better results. Overall, it’s helpful to consume foods in their raw, unprocessed form (when possible) as it is likely that your body will absorb less energy from them. Additionally, more fibrous foods will keep you fuller for longer periods of time. Ultimately though, your gut bacteria may be to blame for weight gain or weight loss plateaus.