Hi Stephanie,
Hope this email finds you well
This last email of yours got me thinking about how now a days everyone is promoting intermittent fasting, 16 hours or more of fasting, very early dinner and late breakfast or skipping breakfast to have lunch directly.
I want to know what’s your take on this.
Thank you for all the content you publish and all the effort you put into giving us updated information.
Have a great thanksgiving.
Kindest regards,
Lucia
A quick primer on what IF is. It is in the category of time restricted feeding, alternate day fasting, and just plain fasting. This just means that you eat your allotted calories for the day within a specific time frame or eating window. This can be four hours, eight hours, 12 hours- basically whatever you choose as long as you eat within that window.
The idea behind this is that restricting your eating window to a specific timeline causes your body to burn fat and it is said to be good for you, your cells, etc.
The caveat here, and this is the case with most research done on humans, is that the subjects of the research or more often than not, men. A woman's biochemistry and physiology is not the same as a mans so the research cannot always translate to what women should or could be doing for better health.
The second issue is that research on intermittent fasting and the benefits of it, is often done on obese and overweight subjects. Almost any dietary changes made to this category of people will indeed show that it can be helpful in improving health outcomes. Men, especially do fairly well on an intermittent fasting diet with improvements in fat loss, blood sugar and insulin levels. Women, however, show no improvements in blood sugar or insulin levels in some studies, according to researcher Dr. Stacy Sims.
Most review articles on intermittent fasting have looked at things like body weight, waist size, blood pressure, heart rate, blood sugar, cholesterol levels, etc. There is little research on the effects that IF might have on circadian rhythms of hormones, including thyroid hormones.
A lot of studies of any kind are first done in a petri dish or in animals, usually rats. Sometimes this is all that is done, usually because it would be unethical to do certain research on humans. These types of studies don’t always translate well to humans. It is something that should be in the back of your mind when you hear things like “Research shows that xyz…”. Always have that critical thinking hat on.
That said, in rat studies, 24 hour fasts lower blood levels of T3, thyrotropin releasing hormone and TSH. In humans, T3 falls pretty fast after a fast. A 3½ day fast in healthy people showed T3 and TSH both dropped within the first two days of the fast. Another study showed T3 dropping by half in 24 hours while TSH remained stable. This is significant for anyone who’s thyroid condition is not already properly managed. And, I’m not sure how long these studies were for. What’s to say that after a year doing this you might also see significant issues with TSH levels. This is the problem. We don’t know because as far as research studies are concerned, thyroid problems are well managed with levothyroxine.
For people doing alternate day fasts from 4 weeks to 6 months long, the amount of T3 in blood was lowered while TSH, again remained the same. Another study showed eight weeks of time restricted feedings for just 8 hours also caused low T3 and normal TSH.
One study in this review showed 6 months of alternate day fasting showed no effects on FT4 or TSH in those with subclinical hypothyroidism. For those that need a reminder, this is when you might be feeling like crap but your thyroid levels don’t present out of the standard lab range so they do nothing for you. This is also when working with a nutritionist is important. Another study though, showed that fasting during Ramadan caused subjects on thyroid meds to need their dose to be raised.
This information is from a review which is referenced on my website with the transcript of this episode in case you want to have a look for yourself. I did not look at the studies mentioned in this review at all. I’m just summarizing what the paper states. If I had a guess, I’d say the studies were not done on women for the most part.
In addition, according to Dr. Sims, intermittent fasting caused more oxidative stress in female subjects where the opposite was true for male subjects. It also slowed production of thyroid hormone and slowed metabolism. Slow thyroid and slow metabolism go hand in hand.
This is a problem for women because when we fast, our body hangs on to fat or tries to hang on to it by slowing things like thyroid and metabolism down. If you exercise and fast together, it makes this even worse. If you are overweight and sedentary, you may see a benefit for awhile at least on the outside but you could be really f-ing things up physiologically.
Same thing applies to the ketogenic diet, another very popular option for weight loss. According to Sims, women’s bodies use carbs to startt hefat burning process and women tend to already be physiologically set to burn fat for fuel but needs those carbs to get things going. She states in her book, Next Level, that the keto diet, even in the short term, may negatively affect bone health meaning causing bone loss which is not a good thing for those of us in post menopause. It might also mess with hunger signals making you feel more hungry and store more fat (another problem for menopause because our satiety signals are not as strong and we hang on to fat much easier). It can also increase cortisol levels which is closely tied to how well your thyroid works.
I hope you found this info helpful. The moral of the story here is not to jump on the latest and greatest health or diet bandwagon. Quick fixes are not long term fixes and they are not a magic pill. The best, most sustainable way to help your chronic health, your thyroid condition, is to make changes you can stick with for the rest of your life. That is what I am here for. You can schedule a discovery call on my website helpforhashimotos.com and we can chat and see if we are a good fit. You can also sign up for my newsletter and get Five Things Your Doctor Won’t Tell You About Hypothyroidism. I’ve been doing a series on mindful eating every Friday in my newsletter as well as a weekly recipe. I respect your inbox and strive to provide you with quality content.
Have a great week!
Welton S, Minty R, O'Driscoll T, Willms H, Poirier D, Madden S, Kelly L. Intermittent fasting and weight loss: Systematic review. Can Fam Physician. 2020 Feb;66(2):117-125. PMID: 32060194; PMCID: PMC7021351.
Kim BH, Joo Y, Kim MS, Choe HK, Tong Q, Kwon O. Effects of Intermittent Fasting on the Circulating Levels and Circadian Rhythms of Hormones. Endocrinol Metab (Seoul). 2021 Aug;36(4):745-756. doi: 10.3803/EnM.2021.405. Epub 2021 Aug 27. PMID: 34474513; PMCID: PMC8419605.