A low-fat/high-fiber diet lowers levels of both estrogen and progesterone compared to a high-fat/low-fiber diet. To little saturated fat has a similar effect on hormone levels. The effect isn't enormous with estrogen being reduced by 7% or more depending on how low fat intake is taken but it does exist. This is certainly beneficial from a health standpoint, in terms of reducing the risk of breast cancer, but it could contribute to the risk of menstrual cycle dysfunction as estrogen will be dropping from a lower starting point under such conditions.
In that they are typically low in fat and high in fiber, vegetarian and vegan diets have the potential to cause menstrual cycle dysfunction
Women on vegetarian diets were more likely to experience them. Perhaps surprisingly, the generally considered to be healthy Mediterranean diet (based around moderate protein, high-vegetable and relatively low-fat intakes) can have the same negative impacts on menstrual cycle function.
While a low-fat/high-fiber intake may be a partial cause, there are other reasons that vegetarian/vegan diets could be contributing to menstrual cycle dysfunction. One is that the nature of the diets often lower calorie intake, which could take women below the critical energy availability threshold (especially if they are active). Limited intake of specific foods such as red meat might also cause nutrient deficiencies (i.e. iron and zinc). In one early study, 25% of amenorrheic women were vegetarian and 100% of them ate no red meat.
Having looked at the potential impact of low-fat/high-fiber diets, I want to look at the other extreme and talk about high-fat/ketogenic diets. These are diets typically containing moderate or high protein intakes, low levels of carbohydrate (50-100 grams or less) with relatively higher fat intakes. Anecdotally at least, there are reports of leaner women who had lost their menstrual cycle regaining normal function when they follow such diets. I tend to think that this is related to these types of diets being higher in fat and often lower in fiber by definition but what little research exists is mixed.
In obese women with PCOS, ketogenic diets have been shown to cause weight and fat loss and improve menstrual cycle function but almost any weight loss in this population has similar effects
In leaner, women Dr Lyle Mcdonald is only aware of a single study. In it, women were placed on a ketogenic diet for the treatment of adult epilepsy (this is one of the uses of the diet) and, despite being at maintenance calories, 100% of them showed some degree of menstrual cycle dysfunction. This is not an ideal model for dieting women, mind you. The ketogenic epilepsy diet is set up differently than the fat loss version and the presence of epilepsy (or use of medications) could have interacted somehow. However, ketogenic diets effectively mimic starvation while eating food but the same overall hormonal responses to starvation are typically seen. Adding to this, the female brain requires roughly 80 grams of carbohydrate per day (in contrast to a male's 100-120 grams) and ketogenic diets automatically provide less than that. If the brain's carbohydrate availability, rather than energy availability per se, is a controller of LH pulsatility, the lack of dietary carbohydrates (along with the brain's shift to using ketones for fuel) might contribute to menstrual cycle dysfunction.
It would appear that both sufficient dietary fat and carbohydrate are required for a woman's optimal hormonal and physiological function to at least one degree or another (sufficient carbohydrate is also necessary to support high-intensity training). And this bring up an issue Dr Lyle mentioned throughout his book: during a diet, due to women's smaller sizes, there is often not enough room to include both in sufficient amounts while keeping calorie intake low enough to generate fat loss.
There are solutions to this address this , which we will cover in later blogs, but this represents another situation that men often don't have to face. Due to being larger and having higher energy expenditures, their diet often allows more than enough room for all the nutrients.
The above information is taken from the The Woman's Book by Lyle Mcdonald with Eric Elms.