New Study Out: Impact of IF on Insulin Sensitivity and Metabolic Markers in Overweight Women
An interesting article popped up in my inbox late last week. New research published in the journal Obesity looks at the “Effects of Intermittent Versus Continuous Energy Intakes on Insulin Sensitivity and Metabolic Risk in Women with Overweight”. The trial was performed in South Australia, enrolled 79 women (average age 50), with BMIs between 25 and 42 (average BMI was 32.2 – obese I). The women were non-diabetic, non-smokers, with sedentary activity levels and low alcohol intake, among other inclusivity parameters.
Over the course of eight weeks, the women were to follow one of four assigned diets: 1) the control (N, 11 women) who were to consume calories to meet their calculated needs with no time restriction, 2) diet restriction (DR70, 24 women) who were to consume 70% of their calculated needs with no time restrictions, 3) Intermittent fasting 100% (IF100, 22 women) who were to consume calories to meet their needs but also fast for 24 hours on three non-consecutive days each week, and finally 4) Intermittent fasting 70% (IF70, 22 women) who were to consume 70% of their calculated needs and also fast for 24 hours on three non-consecutive days each week
The diets, regardless of calorie content, were set to be composed of calories coming from 35% fat, 15% protein, and 50% carbs. The women were instructed to use 7-day food diaries and attend weekly clinics. The aim of the study was to assess the differences in baseline insulin sensitivity, cardiometabolic risk, body weight, and body composition against those observed after the diet trial.
In a very quick summary (click the link to see the full article), the researchers observed that women both on calorie restriction plus IF (the IF70 group) saw greater overall impacts on weight, body fat, and cholesterol levels (all of which were significantly less than they were at baseline), while none of the groups saw a significant change in insulin sensitivity. Thus, they state that, “This study demonstrates that IF approaches using repeated 24‐hour fasts improve metabolic health when in energy deficit but not when in energy balance.”
The researchers concede the following limitations: “This was a short‐term, highly controlled intervention conducted in women. As such, this data is not translatable beyond 8 weeks or to wider populations, including men or those with established metabolic disturbances, such as type 2 diabetes.”
I would like to add the following limitations:
- small sample size, only women, short term trial
- participants self-report (can be assumed that not all reporting was 100% accurate, in regards to energy intake and/or activity level)
- the macronutrients stayed at 15% protein, 50% carbohydrate, 35% fat despite the calorie restrictions
- This seems like not enough protein and too many carbohydrates for sedentary, overweight women
- 15% of protein in a 2000 calorie diet is 75g of protein
- at 70% this is 1400 calories, giving 52.5g of protein
- if the recommendation is 0.8-1.0g protein per kg body weight, and these women are overweight or obese, it seems counterintuitive to allow them only 52.5g protein per day (I don’t actually know the exact amount of protein they were given, this is an estimated number based on the average calorie recommendation)
- This could be why fat-free mass (aka muscle, bone, etc) was not preserved
It would be interesting to see this study retested with changes to the macronutrient prescription. NEXT WEEK: Is IF bad for your gut bacteria?!
Notes and Challenges from Last Week:
I slept better this week, thank God. During a Whole Foods run I picked up this tea with 450mg of valerian root per serving. They recommend 2-3 cups before bed time, but I think that’s just so you go through the package faster / have to restock your stash more frequently. So, I’m sticking with one cup. It seemed to help out more than herbal tea or the “Get Some Zzz’s” Tea from Republic of Tea (which has 45mg valerian root per serving).
Partially thanks to the raisinets allowed last week, I craved sugar on Monday afternoon and indulged in a chocolate chip cookie from the bakery next door. Monday and Tuesday otherwise went as planned. Wednesday morning I waited outside in 24-degree temperatures for a woman who was supposed to show an apartment. When she was 30 minutes late, I left, unable to feel my fingers or toes. Upon arriving home at 9:15am, my face was bright red and I could barely move my fingers, so I crawled into bed fully dressed, including a beanie, under flannel sheets and down comforter to warm up. I woke up an hour later… Instead of heading back out in the cold to hit they gym so soon after warming up, I ate a full breakfast then hunkered down at my work space with a cup of coffee. Luckily these sort of hiccups aren’t too bad since I’m spending a lot of weekday time at home right now.
Thursday put an official end to “dry January” when I had a couple glasses of wine with dinner. Still ended the IF window on time, and was faithful to IF (and dry January) on Friday.
Saturday I just didn’t pack a lunch to take to Athleta (where I work very part time, like once a month) and snacked on a fig-newton type bar during my break. So I was pretty hungry by the time I got home and met a friend for happy hour down the street. This started an evening of eating and drinking with girlfriends until 1am. Thus, IF was not withheld on Saturday since the calories-in window lasted 15 hours (10am-1am). Sunday was a fresh beginning, and I didn’t dwell on my failure.
Sunday I realized that the 12:12 IF pattern actually had another week. Which was nice because I was able to eat between spin class and going to the grocery store and could still eat in the evening during the Chiefs game (which I don’t wanna talk about!). My neighbors invited me over to watch the game and I offered to supply a crockpot chili. It was a holiday weekend and I attended a friends birthday party at a brewpub before going to the neighbor’s, so tack on a soft pretzel and three beers as an afternoon snack.
The plan this week:
Hungry Harvest brought green beans and potatoes this week, so I will be roasting those to eat with chicken. The only meal I wanted to prep this week was chili, which happened Sunday and yielded four servings of leftovers. Knowing the variety of food in my fridge, I will be able to pull lunches together rather quickly. This week I left a few evenings open for dates, but if anything falls through there is plenty in my kitchen to fall back on. So for breakfast, I’ll be finishing up eggs and lentils with veggies and avocado, after workouts I’ll have a smoothie, for a later lunch: chili and salad; and if I need to have dinner at home, I can do veggies with chicken and potatoes. So less planning went into this week but that’s alright.
Next week I’ll be transitioning to 14:10, and I have a lot of stuff in my freezer and pantry to start to work through so that will be a priority. Eating closer to my workouts will be a challenge as I suffer from tummy discomfort if I eat too close to a workout, so I’ll need to find small, quick-burning snacks/meals for morning fuel.