Written by: Kevin Cann
We all know men and women are made just a tad differently. One of the biggest differences being that females go through a 28 day menstrual cycle. Throughout this 28 day cycle the balance of hormones shifts. Can this balance shift affect what macronutrients women rely on more heavily? The answer to that question is yes.
The main hormone I would like to discuss here is estradiol. Estradiol is responsible for the development of secondary female sex characteristics. A female’s level of estradiol typically peaks at the time of ovulation. During this time, when estradiol levels are high, adipocyte lipoprotein lipase (LPL) decreases (http://www.ncbi.nlm.nih.gov/pubmed/7783659 ). This may result in higher triglyceride use by skeletal muscle during this time. One study showed a difference in fuel metabolism during long duration exercise between men and women (http://www.ncbi.nlm.nih.gov/pubmed/9804587 ). Women relied more heavily on lipids for energy than men. Under the same race conditions this study suggests that macronutrient intake should differ for men and women. Women may benefit from a higher fat intake then men running the same race.
Numerous studies have shown that men and women utilize fuel substrates much differently. This may come as a surprise because there is no difference in muscle glycogen storage or GLUT 4 transporters between the sexes. Muscle glycogen is how we store carbohydrates within the body, and the GLUT 4 transporters are what carry glucose into our muscle cells. However, women tend to utilize lipids more and carbohydrates less for energy in relation to men (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2129154/ ).
The differences in substrate utilization may also explain why the birth control pill comes with a side effect of weight changes. Increasing estradiol levels can shift or further enhance certain substrate utilization. Without accounting for this with dietary intervention, weight gain or weight loss may occur. Yet another reason to discuss the pros and the cons of using birth control pills.
In one study done on male rats, 17B-estradiol supplementation increased glycogen sparing and increased lipid utilization during physical activity (http://jcem.endojournals.org/content/90/11/6218.abstract ). This means that when male rats were given the female hormone estradiol, they shifted their substrate utilization to a higher emphasis on lipids. Another study on male rats had similar effects as the previous one (http://jap.physiology.org/content/71/5/1694.short ).
The only time men and women utilize substrates similarly is during exercise intensities of 85% or greater. Both men and women will shift to utilizing carbohydrates as the main energy source. This is due to carbohydrates being the only macronutrient that can be utilized during high intensity, anaerobic training. In any sport or activity requiring less intense and longer duration activity, women will utilize fats as energy more than men, as the previous studies have shown.
During rest women will use more fats from skeletal muscle for oxidation. However, during activity the shift to utilizing fats from adipose tissue occurs. Even when women increased their carbohydrate intake to 75% of daily calories, depending on the phase of the menstrual cycle they were in, there was no increase in carbohydrate utilization or performance (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2129154/ ). Women who are partaking in carbohydrate loading for performance may want to think twice. There are numerous health concerns that can occur from ingesting too much sugar. Women ingesting 75% of their daily calories as carbohydrate to fuel activity may be doing harm to their bodies without the added reward of increased performance.
In terms of performance, as a female, you may need to tinker with various carbohydrate intakes. Understanding the intensities associated with your activity can help. Remember, as long as the activity is 85% of VO2 max or greater, a higher carbohydrate intake may be effective. However, most of us do not continually work at that intensity, and without expensive equipment it may not be easy to determine what your intensity actually is.
There is an increased need for calories if we are physically active. Most supplements and dietary plans focus on increasing carbohydrate and protein intake for this increased need of calories from physical activity. This may not be appropriate for active females, especially depending on where they are in their menstrual cycle. An increase in healthy dietary fats may be more appropriate when estradiol levels are higher.
Carbohydrates are still important though; we need to make sure that muscle glycogen does not become depleted. This will lead to fatigue and decreased performance no matter what. Women may need fewer carbohydrates to avoid glycogen depletion than men. Utilizing the post-exercise window for carbohydrate intake may be the best spot, as insulin sensitivity is increased. This is where the tinkering comes into play. Try different amounts of carbohydrate intake and see what feels best.
Supplementing with MCT oil and/or using coconut oil to cook with may yield an increase in performance. This increase in performance may be more beneficial for women than men. The reason for this is the ketones that are produced from the breakdown of medium chain triglycerides (MCT). They do not require bile salts to be digested. Instead they are carried to the liver and quickly converted to ketones. If women have a higher reliance on lipids for energy then this may be an added boost because ketones are readily available fats. Some studies have suggested that MCT supplementation can increase glycogen sparing and lipid utilization. This may be an even greater benefit for females during ovulation.
Females and males differ in many ways. One way is in their use of substrates for fuel. Women have a higher reliance on lipid utilization then men and men rely more heavily on carbohydrates then women. As a female, tinker with different macronutrient ratios and see how your performance responds. A higher fat and lower carbohydrate diet might be more appropriate. Also, tinker with various ratios throughout your 28 day cycle as preference for substrate utilization may change. I have heard women tell me before that they have it tougher than men, in this case I might have to agree with them!
Thank you for the insight!
Would you consider a Crossfit type workout an activity that is 85% of VO2 max? Thanks
Thanks for recognizing that women aren’t just small men! I have definitely noticed that the affect of different macronutrient ratios on how I feel changes during different parts of my cycle. Most of the time I don’t really go out of my way to eat carbs except after Crossfit WOD’s. But, during my luteal phase if I don’t make a point of getting some carbs every day then I start to feel really fatigued. The first time it happened I didn’t figure it out for a few days and I was miserable. Finally I ate carbs and felt better pretty darn quickly. Subsequent cycles I still sometimes forget this about myself because I love veggies so much I forget to eat something starchy and then I get that feeling again and have to remind myself to carb up. It’s really weird but repeatable enough that I believe it’s a real effect. I wonder if any other women get this?
I’m still intrigued by the carb debate for females and fertility as some of the stuff I’ve read online kinda directly contradicts the idea that lower carb is better for females and my own experience tells me carbs are key to feeling well during certain times of the months. The one thing that makes me really happy about the paleo world is that these debates are going on and information on both sides is available to the public. Debate is healthy!
This makes sense. I’m curious to know if there are any studies in postmenopausal women regarding lipid utilization as the reproductive hormones wane. Or for that matter, are there studies on men in andropause? Since the general health of those in their reproductive years tends to be better in a larger percentage of the population than the health of those in post-reproductive years, I wonder if anyone ever studies the latter group at all!
Finally. I am so tired of all this talk about low-carb vs. high-carb, endurance vs. HIIT, weight lifting vs. body building, carbs post workout vs. protein post workout, fasting vs. regular meal times, etc. etc.
As a female, these debates are damn well f**king useless – 99.9999% of ALL the studies covering these topics are performed using MALE subjects and we just assume that the data applies to women as well, BUT IT DOESNT. As another poster said beautifully, WOMEN ARE NOT JUST LITTLE MEN!!
We need more women involved with science to help highlight the physiological differences between the sexes because if you dig around in the research a bit, the differences between men and women can truly be astronomical, but studies typically just briefly mention these differences and further research into the mechanisms simply does not happen. But who can blame em’? Wouldn’t YOU be more interested in studying your own sex? Women are not involved in research=women being left out of research (unless we are talking breast cancer and/or birth control pharmaceuticals).
I truly believe that there’s a way that women can get the same results as men (same as in same magnitude of change) when in comes to body composition changes, weight loss, performance, etc., BUT ITS NOT GOING TO BE VIA THE SAME ROUTE/MECHANISMS AS IN A MAN. We need more research, more diet gurus acknowledging and debating the physiological difference between the sexes, and finally, we need some diet/training protocols incorporating these differences (and not just that women should start out with lighter weights, more cardio, and a shorter fasting window).
Bottom line;
ESTROGEN CHANGES EVERYTHING.
Oh and P.S.;
To all the diet gurus out there (i.e. Robb Wolf, Mark Sisson, Chris Kressor, Jimmy Moore, Mat Lalonde, LeanGains, Lyle McDonald, Dr. Eades, Peter Attia, Ben Greenfield, Alan Argon, Whole9, and friends [what do ya’ know, all men] );
If you feel that you would be wasting your time, or god forbid ‘losing market-share’, by spending some time looking into these differences because of some false perception that the majority of your followers are men, let me briefly remind you that males currently make up 1/3 of all college graduates. That’s right, 2/3 of all college graduates in the U.S. are now women – and that gap is INCREASING. The tables are well on their way to turning in all academic fields, and if ANYTHING is going to pose a threat to your readership in the future, it’s going to be someone who comes along and ‘cashes-in’ on these physiological differences with the same scientific rigor that you all have brought to the paleo/nutritional community.
Food for thought.
Anyways, thanks for the awesome article Robb. I hope to see more of these in the future. 🙂
As a trans person how do you think I feel? No one ever bothers to study how stuff affects us. Some people say that when it comes to things like nutrition and health we should always think of ourselves as our birth gender. This is direct contradiction to my own experience, but you try and find the studies that lend weight to either arguments. Even stuff which has had a lot of money poured into it such as calorie stuff. “Everyone knows” women need fewer calories than man but there’s no straight answer as to whether as a trans person I would look to male guidelines or female ones. And if it does switch, at what point?
Hormones are a complex thing, and sex and gender are generalizations. Even if differences between “male” and “female” are well understood when it comes to things like nutrition there are always going to be those people who don’t fit into a box.
Sorry rant over. I guess I’m still a little tetchy from my stay in hospital where they tried to constantly feed me tea and toast.
I wonder if this is why some cancers are hormone sensitive.
So if I am reading this correctly, I should try to incorporate more fats into my diet after ovulation. I will give this a go cause after ovulation I am on a downward spiral to carbohydrate cravings that see me throw out the paleo diet 4 days before menstruation and consume loads of bread and sugary stuff but am never able to satisfy my hunger. I do not consume a lot of fats, only what is in the meat and eggs I eat and some olive oil dressing on a salad. Maybe I will start with nut butters and see if this helps the carb cravings.
Thanks for this.
Right?! I think a lot of ladies get ravenously hungry a few days before their period. I know I used to, though when I am eating paleo I find I usually have to *add* carbs before my period, or else I don’t menstruate at all, at least until I have some rice of something. SACRILEGE, I know, but I haven’t found a solution yet. Some sites suggest it’s due to a caloric restriction, but I sincerely doubt I’m eating too little. At 5’0″, it’s tough to do. 🙂 Will try additional fat this month, and see how it goes, but maybe getting carb-crazy pre-period is an indication that we need it? It’s an indication of *something.*
I’m glad to see these issues being addressed. Though I am feeling healthier all around since going paleo, I haven’t had the “miracle” changes that other’s have reported; in fact, I started suffering from severe adult-onset acne. It has taken lots of experimentation with my macros to find what works best for me and I’m still trying to figure things out. Research is all fine and well, but I know that if I go too low carb or maintain it for too long (<100g/day or less) I stop menstruating. I'd love to see future research about the impact of macros on hormones, particularly womens'.
Thanks for this, just in time to prepare for my next period! I always suffer from carb craving during the second part of my luteal phase and the beginning of my periods. Taking Mg supplements helps, and going paleo made my periods a little easier (less painful and less hunger and sugar cravings: before, I would literally cook a huge pan of pasta at midnight!). However, I find it more difficult to remain strictly paleo during that time of the month: I try to silence the cravings by having sweet potato and dried fruit and nuts, but I usually end up buying biscuits or bread at least once or twice, while feeling sluggish at the gym!
OK what about women like me in their 50s? I had a hysterectomy but have both ovaries. I am on the tail end of menopause I guess. My metabolism is stalled. In Texas, I was walking several miles daily, and after relocating to Ohio this fall, that decreased as I had to change my lifestyle. I incorporated MCT and it may have added weight! Not sure, but my physical activity also decreased as the cold weather set in; walking less and less. I just joined a gym so I may find that I will begin to rev up my hormone-challenged metabolism. If I get back into the MCT with a regular workout routine, how much should I be using daily? I was using 1TBLS without any gastric issues. I used it in my AM coffee.