I don’t think I’ve done a research review in a while and even though I imagine some visitors to the site may be getting tired of topics related to the book I’m working on, well, that’s what I’m currently working on so it’s kind of at the top of my mind right now. Today I want to look at how dietary restraint impacts on cortisol levels based on the following paper.
And you can get the free full text here.
A Primer on Cortisol
I imagine most visitors to my site are familiar with the hormone cortisol, even if many aren’t quite clear on what it does. Cortisol is often thought of as a “bad” hormone but this is too simplistic; what cortisol does in the body depends on a host of factors. The primary of these is whether it is released in a pulsatile and acute fashion (basically small pulses) or is elevated chronically. The first situation tends to be adaptive, the second tends to cause problems (for more details check out my still favorite book Why Zebras Don’t Get Ulcers by Robert Sapolsky).
So while acute pulses of cortisol help to mobilize fat, stimulate immune system function and improve memory, chronically elevated levels of cortisol may cause fat storage (especially in the face of high insulin), depress immune system function and harm memory. Basically, acute increases (that go down afterwards) are good, chronic increases (from chronic stress) are bad.
Now another effect of cortisol is to cause water retention; it cross reacts with the aldosterone receptor (involved in water balance) due to its structure. At the extremes there is Cushing’s disease, a situation where cortisol production is out of control and massive water retention is common here. I mean enormous, you can Google up some pictures to see what happens here.
And while I have absolutely never denied that there are other factors that slow fat loss such as metabolic adaptation (a topic I’ve been writing about since at least the early 2000’s), I have argued that the elevations in cortisol in response to diet and exercise (especially when people try to combine a lot of hard exercise with large scale calorie deficits) can cause stalls and an apparent failure of the diet to work. Again, this is by far and away not the only cause of problems while dieting but it is one of them.
And even if Layne Norton isn’t aware of it, we’ve known since the seminal Minnesota study that starvation, and dieting is just starvation on a smaller scale, causes water retention. And let’s keep in mind that despite the name, the men were on 50% of maintenance calories.
I’ve also pointed out that, in addition to certain dieting and training practices, there is a certain personality type that seems more prone to this. When I am being polite about it, I call them tightly wound. When less so, I say they are neurotic as hell. More accurately, they are neurotic about things like their body weight and eating habits. You can always tell these people by the online threads they start. It’s always “WHY AM I NOT LOSING WEIGHT?!?!?”. You can hear the stress in their typing.
This type of personality seems to be far more prone to the type of cortisol mediated water retention that can occur. Invariably when you get them to finally chill out and I have been recommending getting drunk and laid for a while now, they invariably experience a big drop in weight, the whoosh, and their weight drops by several pounds. Which can only be water.
What is Dietary Restraint?
Disinhibition is the tendency to overeat in response to different stimuli, and can occur in a variety of circumstances such as when an individual is presented with an array of palatable foods or is under emotional distress. Restraint is the conscious restriction of food intake to prevent weight gain or promote weight loss, and hunger is the susceptibility to eat in response to perceived physiological symptoms that signal the need for food
Dietary Restraint and Cortisol Levels
The study recruited a bunch of women to take the TFEQ, 666 started believe it or not but they ended up with a fairly small group of 62 women when all was said and done (I have no idea how you lose 90% of your subjects). Their characteristics in terms of age, height, weight, etc. were basically identical.
All subjects completed a 3-day food record to give an indication of their typical diet and were given measuring cups and spoons to get a more accurate measurement. Let me note as always that these tend to be fairly inaccurate.
On the day of the actual urine measurement, food was provided for them to maintain control and no intense exercise was allowed as that alone can raise cortisol levels. Not surprisingly, the high restraint group reported eating about 300 calories less than the low restraint group with no differences in the percentages of protein, carbohydrates and fat.
Urine collections were made within 10 days of the start of the menstrual cycle (this is critical as women’s physiology changes significantly at different times in the cycle) and were measured. That’s really all there was to the study.
A number of different urinary components were measured including cortisol levels, creatinine and calcium and the cortisol to creatinine ratio was calculated. I’ve shown some of the data in the table below including the restraint scores and differences in urinary cortisol levels.
Restraint scores are clearly much higher in the high restraint group and this resulted in about a 15% increase in basal cortisol levels; this was significantly different from the low restraint group.
I’m not sure I have much more to say since I usually do most of my commenting in the background section. And this study was fairly simple in what it did, how it approached it and what it measured. And the results were pretty clear with the high dietary restraint having 15% higher resting cortisol levels. By itself this might not be problematic, but as often as not, these types of dieters are drawn to extreme approaches to dieting and it all starts to add up.
They throw in a lot of intense exercise, try to cut calories very hard (and this often backfires if disinhibition is high; when these folks break they break) and cortisol levels go through the roof. That often causes cortisol mediated water retention (there are other mechanisms for this, mind you, leptin actually inhibits cortisol release and as it drops on a diet, cortisol levels go up further).
Weight and fat loss appear to have stopped or at least slowed significantly. This is compounded even further in female dieters due to the vagaries of their menstrual cycle where water balance is changing enormously week to week anyhow.
And invariably, this type of psychology responds to the stall by going even harder. They attempt to cut calories harder, they start doing more activity. The cycle continues and gets worse. Harder dieting means more cortisol means more water retention means more dieting. Which backfires (other problems come in the long-term with this approach but you’ll have to wait for the book to read about that).
When what they should do is take a day or two off (even one day off from training, at least in men, let’s cortisol drop significantly). Raise calories, especially from carbohydrates. This helps cortisol to drop. More than that they need to find a way to freaking chill out. Meditation, yoga, get a massage. I am not kidding when I recommend getting drunk and laid (perhaps this depends on whether or not the sex is good). Get in the bath, candles, a little Enya, a glass of wine, have some you-time but please just chill.
One last comment, the discussion on this paper had a throwaway statement about the differences in rigid and flexible restraint and how it would be worth measuring cortisol and seeing if there were differences. I’ve only found on paper and it was in post-menopausal women. In it there was no relationship of more flexible restraint and cortisol. Given what flexible restraint describes, this does not surprise me at all.
Which isn’t to say that flexible dieting attitudes, shown to be superior in almost every way, aren’t, well…superior in every way. But they may not mediate cortisol levels. Of course that raises the issue of how much a rigid dieter can adopt flexible attitudes but that’s a different topic for a different day. [FB comments]