A Short Guide To Intermittent Fasting
The benefits of intermittent fasting (IF) are enormous. It can speed up weight loss, enhance mental abilities, and increase lifespan. Here you find why and how to implement IF in your daily life.
Intermittent fasting (IF) is becoming more and more popular these days. It refers to an eating pattern across a 24h period, ideally with more fasting hours than eating.
Different IF methods can be followed, depending on how comfortable you are with fasting and if you ever experimented with it before.
“Beginner”: from 12:12 to 15:9, where the first number represents the fasting hours and the second one the eating hours. Everybody should be pretty comfortable starting with any of those patterns.
“Regular”: from 16:8 to 18:6. Those are the most popular IF patterns, which will also give you the best benefits of IF.
“Advanced”: from 19:5 to 23:1. If you are experienced with IF, you can attempt these methods, but better if occasionally rather than regularly.
Fasting stages
As soon as you stop eating and start your fasting period, your body will enter a series of phases:
Stage I: right after you finished eating your last meal, your blood glucose and insulin levels rise. All the excess glucose will be stored in the liver and the muscle tissue in the form of glycogen, which represents your primary energy storage.
Stage II: as soon as your digestion is completed, usually 3-4h after your last meal, blood glucose and insulin levels start declining. You will start feeling hungry again, as your hunger hormone, ghrelin, increases, and your appetite-suppressing hormone, leptin, declines. If you do not start eating again, your body will start using your glycogen reserves as a form of energy. As a result, blood glucose and insulin levels stabilize.
Stage III: 8-9h after you started fasting, your glycogen storages are depleted, so your body has no choice but to utilize your fat reserves. Fat burning starts, in order to provide energy to the body. It is estimated that an adult with a medium body fat % has ~80000kcal available in the form of fat storage, the reason why it is possible to even go multiple days without eating anything.
Stage IV: after about 11h from the fast start, you enter a phase called ketosis. Your liver produces by-products of fat metabolism called ketones. Ketones will reach all the other organs through blood circulation. The brain seems to particularly benefit from ketones, which exert neuroprotective effects and boost cognitive processes. During ketosis, you might experience a loss of appetite and feel particularly sharp.
Main benefits
Overall, IF induces a multitude of molecular changes in your body, depending also on how many hours you spend fasting.
Regulation of hormone balance: one of the most profound impacts that IF has on our bodies is related to the modulation of several critical hormones:
Growth hormone (GH): it’s one of the most important anabolic hormones, which contributes to, but not only to, tissue growth, fat burning, increased muscle mass, immune system regulation, and cognitive function. IF can acutely increase GH levels (1,2).
Insulin: key metabolic hormone that has a critical role, especially in the absorption of glucose. After at least 8-9h of fasting, insulin levels drop and blood glucose stabilizes, resulting in improvement of insulin sensitivity and increased fat burning (3).
Sex hormones: both androgens and estrogens are affected by IF in males and females. Results are somewhat mixed, but it seems that fasting reduces mostly testosterone levels. While females with conditions like polycystic ovarian syndrome (PCOS) could benefit from it, males might be concerned about muscle mass and libido loss. However, interestingly, in the few human studies performed so far, participants did not report any reduction in muscle mass and libido despite the reduction in serum testosterone levels (4).
Improvement of brain health: fasting can stimulate neurogenesis, a process by which new brain cells are generated. This occurs by induction of a potent molecule known as brain-derived neurotrophic factor (BDNF). Therefore, practicing IF can protect against neurodegenerative diseases and other mental conditions (5,6,7,8).
Extension of lifespan: it might sound like a myth, but IF can actually increase your life expectancy. Even though the majority of studies on fasting and lifespan have been conducted on animals, the results are very promising. It seems that fasting can increase the lifespan of rodents from 13% up to even 83% (9,10).
Cancer prevention and treatment: the preventive effects of IF on cancer are still uncertain and are mostly secondary to the benefits of weight management and metabolic optimization. However, the results of cancer treatment are quite interesting, showing that fasting can work synergistically with chemotherapeutic drugs in reducing tumor growth and chemotherapy-related toxicity (11).
Tissue and cellular repair: IF induces a cellular process called autophagy. During autophagy, cells are able to “clean up” waste material, favoring tissue repair and delaying aging (12,13).
Reduced inflammation: IF can reduce numerous markers of inflammation, positively regulating immune function (14).
Fat burning and weight loss: last but not least, one of the main reasons why people get interested in IF is due to its ability to promote weight loss. Due to the aforementioned effects on multiple hormones, fasting for at least 8-9h induces your body to start getting energy from your fat storage. It is extremely interesting to notice how IF-related fat loss is in particular related to the waist area. Moreover, restricting your eating window can drastically help in creating a caloric deficit (15,16).
Recommendations
How to start IF
IF is considered safe for healthy individuals, but this does not mean that if you have no previous experience with it you should drastically jump into it. Your body needs adaptations to new regimens, so if you are a beginner it is recommended that you start from an “easier” fasting method, such as the 14:10. Listen to your body and check how you respond to it. Once you gained adaptation, you can move to the 16:8 method, which is considered the most popular one for people who practice IF on a daily basis for long-term benefits.
Especially at the beginning of the journey, you might find yourself facing cravings, mood changes, sleep disturbances, and more, which is a normal response to the fluctuations of your blood glucose level, especially when it starts to drop. There are two main ways of overcoming this: drink plenty of water and rely on your mental resilience. If you don’t quit, fasting will become easier after a few weeks.
How to break the fast
When your eating window starts, your first meal is very important. As your body has gone for hours without food, it is highly discouraged to break the fast with large, high-calorie, meals. Avoid foods rich in added sugars, fats, and fibers, or you might end up experiencing stomach discomfort and bloating.
Break your fast with nutrients dense foods rich in proteins, with some easy-to-digest carbs and some grams of healthy fats. A high-protein meal at the end of your fast will boost your metabolism and give you a good kickstart.
The best foods for breaking the fast are eggs, avocados, potatoes, dried fruits, and unsweetened Greek yogurt.
Always remember to listen to your body and take it slow. If you have any underlying medical condition or are on medications, consult your doctor before attempting IF.