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One of the most popular tools natural health practitioners and personal trainers use to help speed up weight loss is something called “carb cycling.” Carb cycling and weight loss have an interesting semi-complex relationship that we will disassemble below.

Carb cycling is where you alternate periods of low and higher carbohydrate content in your diet. This means you might spend five days eating low carb, and then eat more moderate carbohydrate for two days on the weekend.

The theory behind carb cycling and weight loss is that it optimizes your body’s metabolic needs. So the theory goes, while in a low carb period, your body sharpens insulin sensitivity, produces glucagon to help you burn fat, and becomes metabolically streamlined. These are great things. Yet if you persist in being too low carb for too long your thyroid hormone levels will drop, and your insulin sensitivity may actually worsen. In short: you may gain weight.

So advocates of carb cycling say that the best thing you can do for your health and waistline is eat low carb most of the time, but still be deliberate about including carbohydrates every so often.

Honestly, I personally don’t do carb cycling in any serious manner (though I do pay attention to the science I describe to you below), and I don’t recommend it for everybody. (Here are some great fat burning tips I do recommend for everybody).

For a lot of women I work with, it is important to consistently eat carbohydrates.

What women benefit from eating carbohydrates?

  • They are essential for women who have delicate hormonal systems
  • who are recovering from hypothalamic amenorrhea
  • who may have thyroid issues
  • who are pregnant, nursing, or trying to conceive
  • and who have mood issues

Nevertheless, carb cycling is a real, effective tool for fitness and weight loss when used correctly. The problem is that it is not always used correctly. Here’s why, and what to do about it.

1) Carb cycling and weight loss: it’s not gender-neutral

The #1 mistake I see people making with carb cycling and weight loss is inattention to the specific needs of the female body. The idea of carb cycling comes from fitness gyms and online forums (and some scientific studies, though not too many). It is a rather “bro-y” concept.

Because it comes from a world of men, it doesn’t pay a whole lot of good attention to women. But there are two important considerations to bear in mind:

A) Thyroid status must be protected.

Thyroid hormone is essential for fat loss. Unfortunately on a low carbohydrate diet thyroid hormone production can slow down. This is crucial to bear in mind for women especially because women’s metabolism and thyroid activity are much more sensitive than men’s. It is important in the “low carb” times of the cycle to still not be very low carb. Stay above 50 grams of carbohydrate a day, at very minimum (and higher if physically active).

(Check out these documents for more on how to protect your thyroid while losing weight.)

B) Female hormones impact insulin sensitivity

Estrogen and progesterone have significant impacts on carbohydrate metabolism. At different parts in the menstrual cycle, carbohydrates are processed either much more efficiently or with much more fat storage. This is the secret to female carbohydrate cycling. Instead of sticking to a simple regimen provided by a personal trainer or some internet forum, the best thing you can do to maximize the effectiveness of your carb cycling is sync it up with your menstrual cycle.

2) Carb cycling and weight loss: when to eat more carbs

There are two important facts here: estrogen slightly increases, and progesterone decreases insulin sensitivity. 

Estrogen and progesterone are elevated at different points in the menstrual cycle. Estrogen levels tend to be the most dominant in the first and second weeks of the cycle (especially the second week). Progesterone levels are at their highest in the third and fourth week of the cycle.

The consequences of this are that:

  • The female body is naturally more insulin-sensitive in the follicular phase (the first two weeks of the cycle) when estrogen levels are highest and progesterone levels are at their lowest. This means it tolerates carbohydrates in these two weeks better than the rest of the time.
  • The female body is naturally slightly less insulin sensitive when progesterone levels are higher in the luteal phase (after ovulation, in the last two weeks of the cycle). This means it does not tolerate carbohydrate as well in these weeks. Women who are diabetic know this well. I’ve read many studies and heard from many women I know that their insulin injections have to increase in the second half of their cycle because their blood sugar levels are inordinately high.


3) Carb cycling and weight loss: what to do about it

I have talked with fitness professionals like Luke Robinson of Wolf Pack Fitness fame at length about the diet and exercise recommendations they make for women who carb cycle.

They usually recommend that their clients reduce carbohydrate intake in the final two weeks of the cycle, in the luteal phase, when insulin sensitivity is at its lowest. This means that in the first two weeks of the cycle carbohydrate intake might be completely ad libidum or whatever-you-feel-like. That may be too vague for you!

If you want a hard and fast number to adhere to, maybe 35 percent of calories or 200 grams of carbohydrate a day is a good place to start. It can be at its absolute highest in the second week of your cycle, around 45% of calories.

This number varies based on how much you exercise, of course. The more you exercise, the higher that number can be.

In the second two weeks of the cycle, when insulin sensitivity is at its lowest, carbohydrate intake should drop to about 100 grams of carbohydrate a day, which is approximately half of what their clients were doing previously.

The actual numbers are less important to pay attention to than the ratios: insulin sensitivity and weight loss are maximized when carb intake is cut in half in the second half of the cycle.

It is also important to note that I recommend carb levels do not drop below 100 grams a day. That is my preferred number for a lower limit for women, so as to prevent fertility and thyroid problems.

You can find out more about what I recommend for carbs, weight loss, and other paleo tricks, in my extensive book on weight loss for women, Weight Loss Unlocked.

4) Carb cycling and weight loss: fitness recommendations

Fitness gurus also recommend a corresponding shift in type of exercise.

Since insulin sensitivity is at its highest in the first two weeks of the menstrual cycle, and carb intake is free to be at its highest, exercise can be more aerobic (long, moderate heart-rate-elevating cardio exercises). It is at this time that you can do your best high performance cardio training. Here you can challenge yourself with longer-term exercises that may be more “stressful” for your body, like long bike rides, tabata sprints, night-long dance sessions, and the like. It is at this time in your cycle that your body can handle the most aerobic stress.

Since insulin sensitivity is at its lowest in the final two weeks of the cycle, and carb intake is also at its lowest, exercise should be more anaerobic (this means hard and fast, really getting your heart pumping). It should be focused more on high-intensity interval training, with short bursts of high intensity work, either from brief sprint exercises or from weight lifting. This is an excellent way to sharpen insulin sensitivity while simultaneously burning fat, increasing muscle mass, and spending calories. It also helps the body stay healthy and as stress-free as possible during this time in which the body is gearing up to menstruate and the least capable of handling stress.

carb cycling and weight loss

5) Carb cycling and weight loss: the bottom line

I always refrain from providing any hacks or tips I might recommend to shed the “last ten pounds” or what-have-you. I find most of these tips to be unhealthy and antagonistic to healthy weight maintenance in the long-run. Yet even more importantly, I do not want to open doors to you that lead down winding corridors of obsession with weight loss and body image. I know how terrible it is to walk those corridors. I don’t want to be a part of encouraging anyone to do it. In some ways, I consider it my moral duty to refrain from ever facilitating obsession with appearances.

But carb cycling is a nice bit this is one piece of advice I know is solid, and one that I believe can be used responsibly for the sake of how good you feel, how athletic you can be, and also how fit and slim you are. I believe the most important part of your goals for weight loss should be health. Used responsibly this advice can be great for your health, while also—if done so, again, responsibly and with patience and room for less-than-perfect compliance—can be used to keep unwanted insulin weight off your body.

Finally, for more on my unique thoughts on carbohydrates and weight loss for women specifically, check out my program for weight loss, Weight Loss Unlocked! You can read all about it here.

Do you have experience with carb cycling and weight loss, especially with your cycle? How do your hormones affect your diet and fitness?


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