Weight loss
Many people set a caloric intake based on either an estimated or measured total
energy expenditure while they are at calorie balance. Then they work the math on what the deficit should product in terms of
fat loss and go to town.
But between drops in RMR (from
weight loss and the adaptive component), the drop in TEA, changes in efficiency during activity and whatever may happen with SPA, the deficit that is expected and what is actually created may be totally different. I'd note that there are other potential problems here as well, usually related to mis-measurement or mis-estimation (or simply poor adherence) of the day's food intake. I'll have to get Leigh "FatLoss Troubleshoot" Peele in here to talk about that some more.
As an example, consider someone with a maintenance intake of 3000 cal/day when they are weight stable and eating at maintenance. Now they decide to cut
calories to 2500/day, which should yield a nice 1 lb/week
fat loss.
First off, TEF drops by 50
calories/day. If they are genetically unlucky, RMR could drop quite a bit in the first couple of weeks. Their exercise efficiency might go up (meaning less
calories burned during activity) and they might find themselves moving around less during the day due to a decrease in SPA. Suddenly a nice 500 cal/day deficit might be cut in half, the expected
fat or
weight loss will not occur. And that's even before things like water retention are factored in.
I'd note that some goofballs use this response to throw out the
energy balance equation completely, they argue that the calorie balance numbers don't work out because the real
weight loss isn't what's predicted; hence thermodynamics fails.
But this isn't the case; rather, the expenditure part of the equation is changing (usually decreasing) when
calories are reduced and weight is being lost. The equation isn't wrong, it simply isn't static. The value that was your maintenance level when you weren't losing weight isn't necessarily the same as when you actually reduce
calories and start actively
dieting.
Tangentially, I'd note that many people have found that maintenance calorie levels are far more of a range than a value, and this is assuredly related to some of the topics I've discussed above. If someone has a particularly large or NEAT/SPA response in terms of overfeeding, they might find that they are weight stable at a fairly large range of caloric intakes; as their intake goes up, so does TEE due to changes in NEAT/SPA (ok, enough, too many TLAs).
Of real world interest, a number of people on the forum have been playing around with the
Bodybugg (a device worn on the arm that estimates total
energy expenditure based on movement, temperature, galvanic response, and I suspect a bit of voodoo) and some odd observations are coming out of it.
Many, for whom the
Bodybugg shows fairly high maintenance intake values simply aren't seeing the expected
fat loss on what should be a nice moderate deficit. In many of those cases, larger deficits work much more effectively. In general, these are women who, for the most part, have screwy physiologies (and a tenacious bodyweight defense system) in the first place.
For example, one member had a predicted maintenance intake of ~2700
calories per day as measured by the
Bodybugg. On 1600
calories per day, over a 2 month span, the net weight/fat loss was approximately two
pounds. Yet on the very low calorie intake of the Rapid
Fat Loss Handbook program, she lost nearly 4
pounds of
fat in about 10 days. Clearly something strange is going on.
But even more clearly, regardless of the
adaptations to RMR, TEA, TEF and SPA during
dieting, sufficient large deficits can overcome them. With moderate deficits, the changes in those values may cut the deficit to almost nil. With a larger deficit (and a much shorter
diet, mind you; I'm not recommending massive deficits for prolonged periods), this seems to be able to overcome those
adaptations.
Now, I suspect that part of this has to do with some strange goings on hormonally (which I'm currently delving into as one of the never ending projects that consume my days), but some of it simply reflects the above issues. When
calories are dropped, a number of different systems adapt and what was previous maintenance is now lower, what should have originally been a decent deficit no longer is such. Unless the deficit is increased beyond a certain point where the
adaptations are simply overwhelmed by the size of it.
Weight maintenance
Finally, the above clearly has some implications for maintaining
weight loss after the
diet is over (yes, diets do eventually end). Coming out of a
diet, metabolism is going to be depressed, how much will depend on the same factors I mentioned above.
Practically speaking, you can use morning waking temperature to track this roughly. A waking temperature of 97.8-98.2 is indicative of a healthy 'normal' metabolism (i.e. 100% of the predicted value). Every degree drop from that is a roughly 10% reduction from normal.
Some of the drop is unavoidable as mentioned; the loss of
body mass will lower RMR and short of the vest idea, there's not much you can about it. The adaptive component of metabolic rate drop will go away as
calories are normalized and hormones also normalize but there may still be some small reduction in overall RMR even at weight maintenance. TEF should increase as food intake comes up, of course more and/or higher intensity activity can be done when
calories are increased. I'm not aware of anything looking systematically at SPA after
dieting.
In any case, to avoid excessive rebound
fat gain following a
diet, raising
calories somewhat gradually and using a slightly reduced estimate for maintenance is not a bad idea. This can always be adjusted based on
body composition changes. So if you'd normally use 15 cal/lb for maintenance, you might choose to use 14 cal/lb initially at the new bodyweight to take into account the reductions in metabolic rate.
This does mean, mind you, that maintaining the new lower
body weight or
body fat mandates that caloric intake be controlled (or activity increased to compensate for the reductions in metabolic rate). Quite in fact, studies have routinely found that exercise is more effective at preventing weight regain after a
diet more than impacting
weight loss on the
diet.
I'd also mention that both the Rapid
Fat Loss Handbook and my Guide to Flexible
Dieting, have a number of chapters which discuss moving back to maintenance after the
diet is over.
