Most of the nutrition world argues that weight loss is as simple as calories in, calories out: if you expend more calories than you consume, then you’ll lose weight.
But there are a couple of reasons why this isn’t entirely true.
The Thermic Effect of Food
Just like exercise expends extra energy over and above your basal metabolic rate, so does digestion—and while there is a certain fixed caloric cost to certain aspects of this (chewing, peristalsis), some elements depend upon the macronutrient you’re trying to digest. Also, macronutrients inherently carry a different caloric punch as well:
- Protein: there are 4 kCal/gram of protein, and between 20-30% of those calories go toward digestion.
- Carbohydrates: there are also 4 kCal/gram of carbs, but only 5-10% of that is required for digestion.
- Fat: there are 9 kCal/gram of fat, and it only takes 0-3% of that for digestion.
If this were the whole story, then protein would be your best bet for weight loss, while fat would be your worst. And this is true, if you combine fat with carbs (your body’s preferred energy source). Fat by itself, however, or with just protein, actually causes weight loss (which is the whole reason for the ketogenic phenomenon. Click here for more on how that works.)
But there’s one other aspect to keep in mind besides the macronutrients themselves, and that’s the degree to which they’re processed.
Processed Food Takes Less Energy to Digest
This interesting study takes healthy young volunteers and measures their metabolic rate after eating either a whole food based cheese sandwich, or a processed cheese sandwich. (Actually both sandwiches were processed, just to a different degree.)
It demonstrates that the net calories from the processed food are greater than the net calories from the whole food, less the cost of digestion. This makes sense, if you think about it: processed is, in a sense, pre-digested. Whole foods by definition contain more complex compounds, requiring more effort from the body to release their nutritional value.
Hormonal Influences
There’s also the matter of your basal metabolic rate. This is influenced by how much muscle you have versus fat—so the more you exercise, and specifically the more weight bearing exercise you do, the faster your metabolic rate becomes.
But it’s also influenced by hormonal factors.
- Hypothyroidism is most obvious. This controls your body’s metabolic rate. Keep in mind that optimal thyroid levels aren’t necessarily the same as the lab reference ranges! Along those lines…
- Toxicity and poor digestion can lead to low free T3, since T4 to T3 conversion occurs in the liver and in the gut. So even if your TSH and fT4 are fine, if the conversion is off, you’ve still got a problem.
- High reverse T3 which can be secondary to adrenal fatigue, or to inflammation from a variety of sources (or sometimes it’s just your body’s compensation from too-high T4). This can lead to leptin resistance.
- Too-low adiponectin. This is a catch-22 with weight distribution: the less fat you have, the more adiponectin you make, which makes it that much easier to continue to lose more weight. It’s another way in which exercise helps, beyond just increasing caloric expenditure.
The Upshot
If you’ve been frustrated with the idea that all calories are created equal, yet you’re eating like a bird and not losing weight, there really is more to it.
- Are you consuming enough protein?
- Are you consuming whole, unprocessed foods?
- Have you had a full thyroid panel?
- Have you checked your adrenals?
- Are you doing weight-bearing exercise?
