Why diets don’t work: a brief description of Adaptive Thermogenesis from the perspective of your DNA.

Your DNA doesn’t like most diets because most diets imply a significant sustained caloric deficit and the DNA interprets that as a threat against the organism (you) and causes adaptations to occur in the body’s metabolism to counteract that threat—this is the definition of adaptive thermogenesis.

During the initial stages of a significant caloric deficit, which includes fasting, there is not a significant decrease in the basal metabolic rate (BMR), which is the metabolism/burning of the energy stored as fat or glycogen, or ingested energy/food. In fact, there may even be a counter-intuitive increase in the BMR within the first few days before it begins to drop; however, by 2-3 days the BMR does fall precipitously for a host of reasons. There have been some published reports suggesting that the decrease in metabolism is long-lasting and possibly even permanent, but more recent studies have discounted those findings; however, there can be prolonged effects of a diminished BMR, and normalization of the metabolic rate (if it fully occurs) is never as rapid as the initial decrease in it.

In order to fully appreciate this, you need to think like your DNA, which has been programmed to perform automated tasks based upon over 200 million years of evolution. So, when you restrict your caloric intake, your DNA’s initial response is along the lines of get more food, and in order to do that you need to be sharp and fast so you can quickly go and kill something, dig a plant out of the ground, or climb a tree and pick a fruit or berry or nut; therefore, the initial response is to not decrease the metabolic rate, rather, to increase it so that you can kill, dig up, or climb and pick some food. A few days pass, nothing changes, you are still in a caloric deficit; and your DNA thinks uh-oh, something’s wrong, must conserve energy, and the 200 million-year-old DNA automated program triggers a decrease in the metabolic rate to conserve energy to bide time until food/energy becomes available.

DNA: via electron microscope

This is the problem with many commercial diets, and I won’t name names because I don’t want to get into trouble. Typically, these diets might advertise a 10 pound or more weight loss in two weeks. Some of the diets are Very Low Calorie Diets (VLCD), which are sub-1000 calories/day, largely based on shakes and packaged products. Many of the diets include frequent, small-calorie snacks between meals because the volume of food consumed is small and the stimulus of hunger between meals is so great that it needs to be addressed by the snacks  that are perceived and treated as rewards for complying with the severe restrictions of the diet itself.

It is not possible to say exactly how much the metabolic rate is decreased relative the amount of caloric restriction other than the general correlation of the more the deficit, the more the reduction. Again, this applies to a sustained caloric reduction beyond three days. There are ways to counteract the decrease in the metabolic rate such as adding regular exercise above and beyond what you currently are doing (it has to be a change), and some studies have suggested that a high-protein diet can blunt the decrease in the metabolic rate due to a muscle sparing effect.

One of the reasons there is a decrease in metabolism is because of the decrease in the lean body mass (muscle) that naturally occurs with sustained caloric deficits. When your body needs energy, it not only metabolizes fat, it also will metabolize muscle. Since muscle has a higher metabolic rate than fat, when you lose muscle, your metabolic rate drops proportionately. This is why both exercise and higher protein diets blunt the decrease in the metabolic rate—they preserve the lean body mass to some extent.

Other reasons the metabolic rate decreases are related to hormonal adaptations (thyroid), and what is referred to as non-exercise energy metabolism, which reflects muscular activity, like tapping your foot, “nervous energy” fidgeting and other small muscle movements at rest. Also, when you ingest food, it takes energy to digest it, this is called diet induced thermogenesis—it too is diminished with a prolonged caloric deficit.

It is this concept of adaptive thermogenesis that largely accounts for the failure of a diet, the regain of weight, and weight-cycling over a lifetime, going from thin to fat to thin to fat, and back again. This is one of the reasons why there is a failure rate of 80% or more relative to diets and weight loss. It may be that you are in this cycle or are currently struggling with a conventional diet. If you have been on a VLCD, don’t despair, you’ve not done permanent damage, all will revert, if you do the right things.

So, what are you going to do about it?

The primary objective relative to adaptive thermogenesis is to not subject yourself to it to a significant degree. Based on the above, you do this by avoiding nearly all VLCDs. I say nearly all because there are a select few VLCDs that are ketogenic, higher in protein, which are more muscle sparing and therefore have less of a loss of lean body mass and thereby less of a decrease in the metabolic rate; still, it’s a VLCD and in general they are, in my view, unnatural, rather unpleasant, and wholly unnecessary, especially when presented with an easier way.

The easier way is of course abiding by the seven biological truths and ten commandments of The Fat Thief: Take Back Your Life.

One of the commandments is to calculate your caloric needs and aim for a gradual weight loss of 1-2 pounds per week, depending on your start point. If you need to lose a hundred pounds, then aim for 2 pounds per week, if you need to lose 40 pounds, then perhaps somewhat less. It is very important to understand that losing weight is not the only thing, it is losing fat that is everything. It does you no good to lose lean body mass or muscle. It might make you feel better, standing on the scale, looking at a lesser number, but that does not represent a net gain.

If you have read The Fat Thief, you know by now that you can lose fat and not muscle simply by managing your insulin levels, and I go into that in exquisite detail. If you have inadvertently reset your basal metabolic rate lower with a caloric restricted diet, it is by resuming a more balanced caloric intake with a focus on the selective metabolism of fat, as explained in Fat Thief, by which you will re-reset your metabolism to the rate that your DNA, or God, intended although I would qualify that the former does not disprove the latter whereas the latter does support the former. Just say’in.

In summary, minimize adaptive thermogenesis by:

  1. Avoid all VLCDs and aim for a gradual weight loss of 1-2lbs./wk.
  2. Follow the guidelines for managing your insulin levels in The Fat Thief.


Impact of energy intake and exercise on resting metabolic rate.

Adaptive thermogenesis in humans

No consistent evidence of a disproportionately low resting energy expenditure in long-term successful weight-loss maintainers

How is weight loss successful?

Changes in Energy Expenditure with Weight Gain and Weight Loss in Humans