There are several health benefits intermittent fasting provides. Let’s cover the benefits and all the pearls and pitfalls of Intermittent Fasting (IF).
Time restricted eating or intermittent fasting (IF) is probably the most common form of fasting. Practitioners of it often call it by the time ratio of fasting to non-fasting hours. We say the fasting time first, because it is what is important. The fasting period is what provides the health benefits. Popular times are 16:8, 18:6, and 20:4.
There are several benefits to IF including:
Weight loss, improved body composition, improved waist circumference
Blood pressure control
Lower insulin and glucose levels
Increased HDL cholesterol
Anti-Alzheimer’s
Anti-diabetes
Improved immune function
Optimizes sex hormones such as testosterone
Improved microbiome function and biodiversity
Improved cardiac function, improved ionic reserves
Occasionally a news article pops up summarizing a study that attempts to show adverse effects of IF. Many of these studies are only for short periods of time, based on interviewing people and not observing them, missing other confounding factors, and/or looking at a group that already has significant health conditions. The most recent example of this was a study showing adverse effects in people who previously have had a cardiac event. Initial clickbait headlines touted a very high increase in cardiovascular death in people who intermittent fast. When reading more about this study, participants answered two 24-hour food recall questionaires per year. Two. Per year. The study’s analysis was based on 2 out of 365 days of the year. What we know about people is 1 they lie, 2 recall may not be accurate, 3 they try to please the examiner and answer the way they think they want to hear, and 4 when something bad happens (like having a heart attack) they make changes to their diet. Possibly the analysis should be “a little too late to have a benefit.” 1
What are The Rules?
To be successful at IF, there are a few rules to follow. I will discuss these in the setting of 16:8.
The window should start 10am or later. There are several metabolic and added weight loss benefits that occur when the eating window starts after 10am. First, when you break-fast early in the morning, you have a higher rise in insulin than you would have had you ate that same exact meal later in the day. The problem with the higher rise in insulin is that your body will store a higher percentage of the calories from each macronutrient (fat, protein, and carbohydrate), than it would when eating later in the day. Because you are storing more calories, you are also burning less of them.
The window should end 8pm or earlier. Quitting time for IF should not be later than 8pm as there are several things that occur with late eating to wreck your metabolism. Think of 8pm as “sunset.” We don’t honor the sun as all other animals do and we should. Several hormones in our body have surges, peaks and valleys that follow the sun. These are involved in metabolism including insulin, leptin, adiponection, GLP-1, cortisol, and ghrelin. When we feed ourselves after “sunset” or 8pm, our body does not know what to do with it and again, we store a lot more of the calories than we would have had the meal been in the daytime.
Finally the gut microbiome (the very important bacteria in the gut) also follows the sun. On average, the microbiome connsumes approximately 20% of the calories consumed. If you are unlucky, it is lower, maybe 15%. If you are very lucky, it consumes about 25% and you can eat what you want and be svelte. Like you, the microbiome does not want to work 24-7 so it takes a break and says, “No thanks,” when you try to feed it after the sun goes down. The microbiome will still consume calories but a lot less. You see how eating late can add up to extra pounds?
Working a late shift or night shift is a challenge. As discussed above, hormones and the microbiome follow the sun. No amount of artificial light can overide our natural clocks. Yes, you can do IF with a wonky eating window and benefit, but you will not have the maximum benefit and you will be working against your metabolism. Further, cortisol levels will be high at odd times leading to more stress and chronic problems.
The 8 hour eating window needs to be rigid. This means that you are not just eating all of your food in an 8 hour window each day but that the start time does not change. An example of breaking this rule would be to have breakfast at 8AM (because you are meeting friends) and eating until 4pm. Tomorrow, you plan to start eating at noon and stop at 8pm. This weekend, you’ll have a day when you start at 2pm and stop at 10pm but the next day you will do brunch at 10am and stop at 6pm.
In the fasting window, consume only water, black coffee, and plain tea. Consuming any calories, will cause insulin to rise. Protein and carbohydrates cause insulin to rise and should be avoided completely. Although fat (such as putting heavy cream or butter in coffee) does not cause insulin to rise, it does affect other metabolism hormones as listed above and will put a pin in the mobilization of fat stores. During the fasting period, this is when the body should be mobilizing fat stores for energy, not processing ad using macronutrients coming in.
People often ask if it is fine to add lemon to water and other beverages. As sour as it it, a lemon has 5 grams of sugar. It is best to avoid lemon in the fasting window.
No zero calorie articial sweeneters or zero calorie natural sweeteners in the fasting window. Better to avoid them altogether. Stevia, xylitol, sacarrine, aspartame, monk fruit, sorbitol, and any other you can think of are a problem. Sweeteners that have no calories have been shown to increase weight gain in people. Why does this happen? Although these products have no calories, your body still sees them as sugar. This means that insulin will rise. Again, when this happens, your body prefers to store calories instead of mobilizing them from fat stores. Definitely avoid these products during the 16 hour fasting period and use them with caution during the eating window.
University of North Carolina at Chapel Hill has created a guide to all of the chemical names that mean zero or ultra low calorie sweeteners. See the link at the end. 2
Not eating enough food/calories. People who struggle to lose weight while doing IF may not be eating enough calories, especially fat calories. When you do not eat enough calories, your body feels that it is starving resulting in a significant metabolism slow down. When the “starvation period” ends, the pendulum swings the other way and the body tries to make up for the period of insufficient calories resulting in an increased appetite and the body going out of its way to store more fat while metaboism continues to be slow.
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