I ranted a little about diet approach, leptin and the set-point theory on bodybuilding.com.

Figured it could make for a decent post here. I added some extras in the form of a short review on the effects of intermittent fasting on leptin.

Short background on leptin and set-point

Leptin is a master-hormone with downstream effects on other hormones related to metabolism (T3/T4, neuropeptide-Y, epinephrine, among many others).

In the long-term, leptin is regulated by total amount of fat mass. A drop in leptin affects the other hormones negatively and vice versa. Low leptin leads to an increase in hunger and a decrease in metabolic rate, much like high leptin leads to a decrease in hunger and an increase in metabolic rate.

Generally speaking, lean people have low levels of leptin while obese have high levels of leptin. However, in the latter case, leptin resistance develops. This is likely an effect of chronically elevated leptin, much like insulin resistance is an effect of chronically elevated insulin.

The set-point theory of body weight-regulation is intimately connected to leptin and has a strong genetic component to it. Naturally lean people maintain a low body fat set-point by being leptin-sensitive; they can maintain a low body fat percentage and function optimally even with low leptin. But most of us aren’t so lucky, which is why getting really lean is typically a difficult task.

Dieting in the single digit body fat-range

Lyle McDonald paints a dark picture of life in the low body fat percentage-range. Yet I and my clients maintain a low body fat % without any of the often cited symptoms, such as anhedonia, low libido and a general sense of weakness. It’s hard to argue against the literature on the topic, since it’s substantial and shows that these side-effects indeed occur. However, it bears mentioning that the studies looking at leptin levels after dieting are limited in the sense that they often use conventional dieting strategies that entail a pronounced weekly calorie deficit for both men and women.

I too experienced the aforementioned side-effects in the past, That is, before I finally “got it right.” What does that mean exactly?

Me at a skinny 165 lbs. Editorial work in Milan. My approach to dieting back then wasn’t exactly ideal.

During my last cutting diet, that is the one that took me to 5.5% where I have hovered ever since, I did the following things right:

  1. I lost the final pounds of fat very slowly and the weekly calorie deficit was subtle. The scale moved down as slow as one pound every other week. On the other hand, I barely felt like I was dieting and I maintained strength and muscle surprisingly well.
  2. I was able to make a smooth transition into maintenance. I did not count the days until the diet ended, and I did not sit and plan a big refeed to celebrate when I was done. I didn’t feel deprived, daydreaming about food.
  3. I would do a extremely controlled and modest refeed 3x/week or 3x/8 day (on training days).

Now contrast this to what I did in the past, which caused me to feel miserable during the whole process and experience rebound weight gain:

  1. I wanted to lose as fast as possible so I could work on muscle gaining. The weekly calorie deficit was fairly substantial given my already low body fat percentage – I was losing in the range of 1-1.5 lbs/week. I felt deprived and just wanted to get it over with. Strength and muscle loss was substantial.
    Another one. From a shoot in Münich. Weight around 165 lbs or so.
  2. I would sit and plan my big refeed meal at the end of the diet. I would count every day like an inmate counting the days to his release from prison. And once I reached my goal, I would go bonkers, eat a bunch of crap, take several steps back and then go back to dieting in a feeble attempt to make up for my screwed up “refeed” (aka binge in my case).
  3. I did no refeeds during the diet.

So what’s the lesson here and how does it relate to the topic at hand?

Leptin: science versus real world

Leptin is controlled primarily by two things, which are

  • a. Short term: acute energy balance. A high calorie deficit causes leptin to drop lower than what can be explained by fat loss, and a caloric surplus raises leptin higher than what can be explained by fat gain.
  • b) Long term: total amount of fat mass. Fat cells are factories for leptin production. Not having many factories obviously impairs production and the aboslute amount of leptin in circulation.

If A can be manipulated via a subtle energy deficit and regular refeeds of the right macrocomposition (carb refeeds acutely increase leptin, while fat has no effect), this should prove beneficial to circulating leptin levels during the diet. It might prove fruitful to “trick” the last few pounds of fat off while venturing into the single digits. Another cyclical diet that has much in common with this strategy is The Ultimate Diet 2.0 though I’m in favor of more frequent, more modest, refeeds and no glycogen depletion outside what occurs with a low-moderate training volume.

If anecdotal reports mean something, this is my standard approach for clients and it’s working well. I’m not an isolated case. For example, have a look at Andreaz in this post on maintaining low body fat. And we’re no ectomorphs by any means. I grew up fat. Science dictates I wouldn’t be able to stay this way (low body fat) without feeling completely miserable, but that’s just not the case. The avatar pic was taken at the end of 2007, and I’ve stayed that way ever since. But I failed many times in the past. Only when I learned patience did I attain my goal.

Now, this little theory of mine, that fat needs to be lost very slowly in the single digit range, still leaves questions as it pertains to B, which is that leptin is ultimately controlled by total amount of fat mass.

Several years and 30 lbs later, I finally “got it right”.

Low fat mass equals low leptin. Can leptin sensitivity increase if weight is maintained on a low body fat % for a prolonged period of time? Sadly, there are no studies to suggest that for the time being. Can it increase through other means? Well, exercise and fish oil seem to improve leptin transport, so there’s that.

But what I think people really want to know is how intermittent fasting affects leptin levels and there’s some interesting research on that topic.

Intermittent fasting and leptin

Generally speaking, studies show a neutral effect on average leptin levels during intermittent fasting. While the fasting period decreases circulating leptin, this is compensated by a big boost when refeeding. In comparison to conventional meal frequencies, intermittent fasting induces a “peak and valley”-pattern in leptin synthesis. Leptin secretion is thus entrained to the meal pattern and shifting meal timing causes a comparable shift in plasma leptin rhythm.

However, there are some interesting discrepancies here in that women actually show a big increase in mean leptin levels during intermittent fasting. This occurs even in the absence of weight gain which is all the more fascinating. In the quoted study, despite calorie intake being elevated in comparison to baseline intake, the women actually lost weight and lowered waist circumference and body fat percentage. Intermittent fasting was also shown to decrease neuropeptide-Y, a hormone that stimulates hunger. This could probably be explained by elevated leptin levels, but there was no linear correlation between the two in this case.

Similar effects have also been shown to occur in men. That is, fat loss occurred without any reduction in leptin – and these were fairly lean athletes to begin with.

Intermittent fasting may also be of benefit when dieting in the single digit range due to the effect of fasting on the fat mobilizing hormones epinephrine and norepinephrine. When you’re in the single digit body fat range, you’re likely to have low circulating levels of leptin. One of leptin’s downstream effects is on epinephrine and norepinephrine output. Low leptin equals impaired output of the aforementioned hormones. This is part of how leptin regulates metabolic rate. However, it seems that these hormones increase regardless during fasting. That is, leptin is not able to exert it’s usual power over these hormones. In this case, their increase cannot be mediated by leptin which allows fat mobilization to go on unabated during fasting.

That’s it for now. There’s plenty more on this topic, but I’ll save that for some other time.


  • Fat loss in the single digit body fat-range needs to be slow and tempered. In my experience, this allows for a smooth transition into maintenance and minimizes muscle loss. I also believe it might lessen the negative effect of dieting on leptin, which ultimately makes maintenance of low body fat achievable. I think most people diet too hard, which has a profoundly negative effect on leptin – and this is part of the reason why the weight gain rebound is so common in folks who finally manage to reach their goal (and then screw up everything by binging).
  • Planned and regular refeeds should be in place. This affects leptin positively and allows for maintenance of muscle and strength. Even if your goal ultimately is fat loss, entering an anabolic phase with post-workout overfeeding will serve you well.
  • Intermittent fasting seems to have interesting effects on leptin synthesis. Whether this has benefits for low body fat maintenance or circulating mean leptin levels is up for speculation for the time being.

For more on leptin and set-point, read this and this. I’ve also talked about the effects of our obesogenic environment on set-point and weight regulation in this post. Somewhat related to the topic at hand, I’ve also posted on strategies for maintaining low body fat.

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