Last week, we went over the cruelest fact of weight loss: your body is actively trying to stop it from happening. Losing weight causes a metabolic slowdown above and beyond what you’d expect from simply losing the extra mass – a person who dropped from 200 to 130 pounds has a slower metabolism than a person who has always been 130 pounds.
This is probably related to a decrease in the thyroid hormone T3, although it’s not quite clear how that translates into a slower metabolism. It’s probably not a reduction in resting metabolic rate (since low-carb diets reduce T3 without affecting RMR), but it might have something to do with how efficiently your body uses food for energy.
Part 1 was the theory; now it’s time for the practical: if you’re eating Paleo for weight loss, what can you do about it?
Does Pace of Weight Loss Matter?
Your first instinct might be to go for a “slow and steady” approach so your body doesn’t freak out about it. In many of the studies where weight loss caused a metabolic slowdown, the subjects quite rapid and even extreme weight loss (one was basically the equivalent of The Biggest Loser, which is about as far from a healthy or sustainable approach to losing weight as it’s possible to get).
So can this all be avoided by going at a more moderate pace? It's hard to tell; there aren't a lot of studies comparing slow and fast weight loss. This study found that even a very moderate and slow weight loss (about 14 pounds in 1 year, which is just over 2 pounds per month, hardly a crash diet) caused decreases in T3 proportional to the amount of weight lost. This suggests that even a very slow pace of weight loss won't entirely eliminate reductions in T3.
On the other hand, slow and steady weight loss can help you preserve more of your muscle mass, which is huge for long-term success even if it doesn’t influence T3 production (more on this below). It can affect other gut and appetite hormones. And it can also have psychological advantages – for example, if it’s less painful, it’ll be easier to keep up in the long term, which is a huge benefit. So in practical terms, slow and steady may still win the race. But holding everything else constant, slower weight loss per se isn’t a magic bullet for avoiding T3 reductions.
Another obvious question is whether any particular diet can be helpful. Can you prevent metabolic problems by tweaking the protein-carb-fat ratios? What about micronutrients?
In terms of macronutrients, finding a carb level that works for you is key. Low-carb diets typically reduce T3 production, which doesn’t help much with the metabolic slowdown issue, but if they help you stick with it in the long run, the metabolic disadvantage may be outweighed by the all-important advantage of long-term adherence. Higher-carb diets keep T3 higher, but it’s always a balancing act against other factors, like insulin resistance, cravings, and hunger.
Eating enough protein can help regardless of carb level, because it increases the amount of energy you need to spend digesting the food, which ends up increasing your metabolic rate. But this effect is small in the grand scheme of things, and if you’re eating Paleo anyway, you’re getting plenty of protein and there’s no need to stress about supplements or protein powders.
Macronutrients can also help in terms of managing leptin levels. Leptin is another hormone involved in weight loss; you can read about it here. Maintaining leptin levels may help maintain thyroid hormone levels (and also make you less hungry as a bonus). One major strategy for keeping leptin stable during weight loss is to occasionally do a higher-carb, higher-calorie re-feed, even if you normally eat lower on the carb spectrum.
In terms of micronutrients, Iodine is important for good thyroid health, and a lot of people aren’t getting enough of it (although too much can be just as bad). Iodized salt (not sea salt), fish, and seafood are all good sources.
And then there’s this great study: beef, green vegetables, and butter as a very tasty and effective thyroid-healing diet. Sounds like Paleo!
Exercise, especially strength training.
Another great strategy for reducing metabolic slowdown is to exercise. Exercise helps maintain metabolic rate and prevent metabolic adaptation to weight loss.
Partly, this is because it preserves muscle mass, so more of the calories you burn come from fat, not from muscle. In the short term, this actually slows weight loss a little, because 1 pound of fat stores more calories than 1 pound of muscle, so it takes more days of a calorie deficit to burn a pound of fat than it does to burn a pound of muscle. The more of your calorie deficit that you “spend” on burning fat, the more slowly the number on the scale will go down.
But in the long term this is actually a good thing: remember that body mass is one of the biggest determinants of resting metabolic rate. Preserving your lean tissue (aka muscle) helps keep your resting metabolic rate higher – and if your goal for weight loss is to look better, keeping your muscle will also help with that. Muscle mass is the mass that makes you look good naked – yes, even for women; “muscle” does not equal “bulky” unless you’re also doing some serious steroids. And even beyond aesthetics it’s also very good for your health in all kinds of other ways.
So preserving muscle mass keeps the mass that makes your body look good, while limiting the damage to your metabolic rate; it’s a win-win. Any kind of exercise is great, but resistance training (heavy weights) is particularly effective for building muscle mass.
The Usual Suspects: Sleep and Stress
This one is easier said than done. Your thyroid doesn’t like stress, and it doesn’t like sleep deprivation. If you want to lose weight, you want to keep your thyroid as happy as possible, and you certainly don’t want to reduce T3 levels even more than you already are by losing weight. You know the drill: 8 hours a night in a dark room, and practice some form of stress management that works for you. If that’s just not going to happen, try reconsidering your priorities, and if the things keeping you up at night really are more important to you (sometimes that does happen!), here’s how to do damage control.
Summing it Up
Weight loss is metabolically painful. Exercising while you lose weight, eating enough protein, managing lifestyle factors, and paying attention to diet quality (especially iodine and finding a good carb level for you) can help minimize the metabolic damage – it really is about so much more than counting calories that you eat and burn.
There’s also a lot of individual variability in the metabolic effects. In all the studies in Part 1, the variation in the metabolic drop was pretty big, enough that the people on extreme ends of the spectrum would have pretty different experiences with it. You might be one of the lucky people who get a very mild slowdown or even no really noticeable issue at all. You might also be one of the unlucky few who really struggles.
Everyone is different, but from what we know about diet and the thyroid, Paleo looks like as good a diet as any for minimizing thyroid problems during weight loss and hopefully preserving metabolic rate as much as possible.