Following on from the couple of blogs I wrote about Dan’s LCHF athlete lifestyle, I got a lot of messages from women regarding my opinion of it for the female endurance athlete. Great question, especially as – if you look at social media – there are nutritionists who warn against the danger of LCHF (and intermittent fasting) for women, to the point that the blanket statement is that it is harmful and not to be undertaken. Whilst it is hard to be objective in the nutrition space – all of us influenced to some degree by our own experiences – the low carbohydrate and fasting space seems to bring with it its own special degree of hysteria. The prevailing message is that both low carbohydrate diets and fasting is too stressful on the endocrine system of females (which regulates hormones) and causes a reduction in metabolism and reproductive potential. Thus, it is to be avoided at all costs. This point of view may be drawn from clinical experience of the practitioner and be dependent on the type of client they see. If their target audience are women who have struggled with maintaining a healthy weight and have problems with eating enough, then the opinion of the practitioner could well be influenced by this (and is entirely sensible!) Likewise, I see many women who’s hormones benefit from periods of intermittent fasting while utilising a LCHF protocol. What we see in clinic will dictate our points of view, regardless of how objective we try to be.
I have in the past written about the negative impact of fasting and calorie restriction on the expression of genes that regulate kisspeptin in the body, a hormone involved in our reproductive cycle. However I will point out that the effects seen in studies conducted in rodents may be more dramatic than if they were carried out as clinical trials in humans. Rodents have a much faster metabolism, thus a 24h fast for a mouse is equivalent to a 3 day fast in humans. Likewise, chronic caloric restriction over a week, where the mice lose close to a quarter of their body weight (and which is thought to be responsible for the downregulation of the kisspeptin receptors that result in negative effects) may be equivalent to 12 or more weeks. Rodent models in science are great for illustrating potential mechanisms, but can never be viewed as hard data as it pertains to humans.
Alongside any scientific data that exists, I think it’s important to step back and consider perspective here. What we should all be aware of is that there is no one right dietary approach for everyone, and often there is no one dietary approach to suit someone for the rest of their lives. As things change, so do our nutritional requirements. Low carbohydrate diet and intermittent fasting is not exempt from this – therefore to say that it is not suitable for any woman is, quite frankly, erroneous and misrepresents what we see in the literature and what we see clinically. While certainly a vast majority of the studies investigating lower carbohydrate diets have been conducted in males, there are studies showing a positive impact for overweight women with infertility. Further, it is accepted best practice to include periods of low glycogen availability in the training schedules of athletes. Even in the researchers who err on the side of pro-carbohydrate diets recommend cycling carbohydrate intake to be sometimes low, and sometimes high, to upregulate fat oxidation pathways that allow the athlete to become more efficient at burning fat. To state that no female athlete should start an exercise session in a fasted state goes against current best practice for endurance performance.
Possibly the negative impacts of fasting and low carbohdyrate diets are not about the fasting period or the carbohydrate content – it’s much more likely to represent chronic underfuelling – i.e. a lack of calories over an extended period of time, with no thought given to cycling of both energy intake and/or macronutrients. It’s just low, full stop. That’s why it is important to work with an experienced sports nutrition practitioner (like me, Kaytee Boyd, Caryn Zinn as some top picks) to ensure these training tactics are used to the advantage of the athlete in a training cycle, not to the detriment of them.
Don’t misread this as a recommendation to do all sessions in a fasted state, to undergo an intermittent fasting protocol that involves skipping breakfast every day of the week, or that everyone should adhere to a very low carbohydrate approach. If you’ve read any of my information (or followed anything I’ve suggested) then you’ll know this isn’t the case. The point of this blog is to remember that there is no one right dietary approach for everyone, and that if you’re successfully adhering to a lower carbohydrate diet with periods of intermittent fasting and feel it’s working well for you (ie no sleep, hormone, training or recovery problems), don’t be concerned with the rhetoric that exists regarding the harmful nature of this. You are your own best investigator when it comes to your nutrition, and your experience is the most important data when it comes to you.