Updated: Mar 7
In Part 1, we told you about what Intermittent Fasting is, now we’ll dive into how it works.
How does it work?
The goal of IF is to reduce insulin levels. Insulin is the key hormone produced by your body when digesting food – it works to store excess fuel in the body. So, if we can reduce the levels of insulin by fasting we can allow the body to consume some of that excess fuel (i.e. fat).
By minimizing insulin stimulus, we are allowing our bodies to burn more fat rather than sugar. Most of our bodies have become very efficient at consuming carbs to produce sugar as energy. When we fast, we are retraining our bodies to consume fat to produce ketones as energy instead.
If you think about it, human beings evolved with long periods of starvation during the millennia that our ancestors lived as hunter-gatherers. The concept of having an abundance of food with regular meals only came about with the advent of agriculture in recent decades.
Turns out there are many different levels of hunger, just as there are many different levels of full. It’s a good idea to become attuned to the signals that your body is giving you and to learn how to assign a number value on a scale to that physical sensation. Like there’s “I’m too full to eat any more and it would feel good to go for a walk” (80% full) and then there’s “I feel uncomfortably full and can’t really get up” (120% full).
I used to find that hunger signals could be confusing to interpret. They could be:
physical hunger (like when I hadn’t eaten in >5 hours);
thirst (i.e. dehydration from inadequate fluid intake);
emotional hunger (e.g. stress, boredom, anxiety, loneliness, you name it); or
Withdrawal (a.k.a. “hangry” or voracious hunger occurring only a couple of hours after a meal, caused by carbohydrate withdrawal/craving).
Practicing intermittent fasting has allowed me to become “fat-adapted” so that I am more able to read and respond to my body’s cues.
The principle behind the “fasting mimicking” approach, as promoted by Dr Valter Longo, is to use certain foods strategy to promote satiety while encouraging the body to remain in a fasting metabolic state. We want to break the cycle of addiction to carbohydrates.
Insulin levels spike in response to high carbohydrate intake, but when those levels fall off we end up craving more carbs which in turn leads to a vicious cycle and eventually insulin resistance.
While there are many approaches to fasting mimicking, I have found that “fat fasting” is a good way to ease into it. The more that you can teach your body to use fat as a fuel, the more “fat-adapted” (aka “in ketosis'') you will be, and the less ravenously hungry you are likely to be even several hours after the last meal. And if you do get a little hungry, you can have a “fat snack”.
What’s a “fat snack”?
When you are hungry during a fast period, try reaching for a “fat snack”, like 1-2oz of nuts. Brazil nuts are my favorite because they are filling, and you won’t eat too many. Or consider half an avocado, one whole hard-boiled egg, 1-2 oz cheese, or healthy peanut/almond butter.
Give yourself about 30-60 minutes after consuming the “fat snack”, to gauge your hunger level. If you are still very hungry, you may want to have a meal like a salad or soup. If you are only a little hungry, you can add another “fat snack”, or try a “fiber/fat snack”, like celery stick with cream cheese, or chia pudding with coconut milk.
Our bodies tend to do best with gradual adaptation to fasting, slowly extending the fasting time from 12 hours, to 15 hours, and so on. Dehydration and salt deficiency are common early pitfalls that can cause discomfort or lightheadedness, so be sure to consume at least 8oz of water every 2 hours, adding in a sprinkle or two of salt when needed. Your body and brain will thank you..
Please note that our bodies are all different and will respond differently to various eating plans. Dr Em is a doctor, but she is not your doctor. You are advised to seek the guidance of your licensed dietician or doctor before embarking on intermittent fasting if you have diabetes, are taking any medication, are training for an athletic event, have experienced an eating disorder or have any other health issues. Ketosis and dehydration can be dangerous in certain medical conditions.
The Obesity Code by Dr Jason Fung is an excellent summary of the science behind intermittent fasting as an evidence based approach to weight loss and blood sugar management.