Intermittent Fasting: Is it good for women?

Intermittent Fasting has many supposed benefits – a major one being weight loss.  Thanks to one of my patients, it was brought to my attention that Intermittent Fasting has potentially-different effects on men versus women e.g., having effects on the menstrual cycle.

As most of you know, IF doesn’t tell you what to eat as much as when to eat.  The idea is that short-term fasting is healthy – and for the most part, this appears to be the case.  As with anything else in life, however, IF is not good for everyone at all times, and women, in particular, at certain times in life e.g., pregnancy or when stressed.

The problem with the literature is two-fold:  1)  there is no standardization as to what IF regime they are studying.  For example, most of the literature that I reviewed uses “alternate-day” fasting as the benchmark.  Other IF regimes, like the Crescendo Method (fasting 12-16 hours for 2-3 days per week e.g., Monday, Wednesday and Friday) or the 5:2 Diet ( fasting for two days per week, restricting your calories to 25% of your usual intake) have not been extensively studied, and 2)  most of the studies have been done on mice/rats.

Many women have reported that certain types of intermittent fasting has caused sleeplessness, anxiety and irregular periods.  There is also a physiological state called “metabolic distress” – which involves the activation of the “hypocretin neurons” in the hypothalamus (this happens when the body perceives that it is in a “starved” state).  It is well-known that caloric restriction beyond a certain level i.e., starvation is terrible for a woman’s reproductive system and can create hypothalamic amenorrhea or the shutdown of periods, for example.

Fat stores are very important to maintain regular menstrual cycles.  This is why women have more fat under the skin than men.  It is also why women get cellulite and men, for the most part, don’t.

If we use the alternate day IF regime in female rats, the result is clear.  “For female rats, the degree of change in brain chemistry and in behaviour was directly proportional to degree of calorie intake, demonstrating the unique sensitivity of female rats to the starvation response”.  Interestingly, both female and male rats gained small amounts of weight on the alternate-day IF diet, and male rats became more fertile (while female rats became infertile).  For female rats, even a 20% caloric restriction increased the proportion of animals “displaying irregular cycling patterns” At 40% CR the major of the female rats ceased to cycle at all.  If we extrapolate to human females, CR increases the likelihood of irregular periods or the cessation of periods.

Human studies have shown that:

  1. Alternate-day fasting can create harmful metabolic effects in women;
  2. Alternate-day fasting did NOT improve insulin sensitivity in women (as it did in men);
  3. Alternate-day fasting had an unfavourable effect on glucose tolerance in non-obese as compared to obese women;
  4. Overweight and obese women appear to have some significant improvements with IF regimes, but normal weight women may not.

For those of you who have seen my previous blog on IF, I believe that we have to “follow the light”.  Our circadian rhythms are tied in to the light dark cycle on a twenty-four hour clock.  When it comes to eating we, as humans, are only meant to eat between sunrise and sundown – and to rest and restore between sundown and sunrise.  Our dependence on artificial light devices like tablets and cell phones has disrupted our internal regulation.     Intermittent Fasting should follow these cycles.

Intermittent Fasting to me is not Caloric restriction but Carbohydrate Restriction.  The IF schedule for me is to restrict carbohydrate consumption to 8 hours in the day in order to flip into fat burning mode.  Carbohydrate Restriction is NOT Calorie Restriction – unless all your calories are coming from carbohydrates.  Consuming carbohydrates is far too easy.  This is a problem, because most of us are not used to getting our calories from good proteins, non-starchy vegetables and fats.

I have found some glitches, however.  I have subconsciously accepted the notion that to lose weight you have to calorie restrict – so I found myself eating less than normal during the day which affected my energy levels dramatically (and not in a good way).  The point of IF is to enter ketosis for several hours to force the body to use fat stores for fuel not to reduce calories or “starve” yourself.

In addition, certain individuals have trouble digesting and metabolizing fats.  Not only do they have to learn to eat better sources of good fats, they may have to take digestive enzymes to help digest the fats then optimize the fatty acid metabolism by using certain supplements.  CoQ10 is one of these supplements (which is low in 50% of individuals who are overweight).

I have also found that stress kills the effect of IF.  Stress increases cortisol levels which releases glucose from the liver into the blood.  More glucose in the blood releases insulin.  More insulin takes excess carbohydrates and stores them as fat.  To allow the IF regime to work, stress levels must be controlled – and this is especially true for women.

Intermittent Fasting for women in summary

  1. Women are different than men in their reactions to IF;
  2. Obese women may benefit from IF more than non-obese women;
  3. Women should probably not use the alternate-day IF regimen, or any IF regimen that involves fasting for 24 hours;
  4. If you are female, Do NOT caloric restrict in general more than 10% of total calories. Female bodies are extremely sensitive to caloric restriction;  Make sure that you have an adequate caloric intake during the non-fasting times;
  5. If possible, substitute good fats for carbohydrates to a large extent – if you are attempting to lose weight;
  6. If you cheat, cheat ketogenically – to maintain the carbohydrate restriction of 8 hours i.e., eat proteins and good fats;
  7. If you are pregnant or planning to be, are breast-feeding or have any medical condition involving disruptions in glucose (like hypoglycemia) or in fat metabolism, or have an eating disorder, sleep problems or are chronically stressed, please discuss your situation with your health care provider before starting a fasting regimen of any type.

Dr. G