The word fasting has gotten a lot of attention lately. Maybe because it seems like a quick way to lose weight to some people. Healthy weight loss is much more complicated than simply fasting and eating nothing. There are many ways to incorporate fasting into your life; however, you want to pick the right type of fasting for you to match your goals.
1. FAT FASTING
Fat Fasting also is very popular in some keto communities. Sadly, this is another terrible piece of advice when it comes to finding health and weight loss. Here are some of the issues with fat fasts.
First off, the scale can and will show a drop in weight when you lose muscle mass. This is not a good thing. Muscle is precious and you can’t build muscle on fat alone. Only amino acids in the diet plus strength training builds muscle. Your body can not make muscle from fat and your body is turning over protein cells every day (think how much skin is shed, etc, more below in the long-term fasting section).
A fat fast will result in a loss of lean mass as you are eating no protein. This lowers BMR as you have less muscle-using energy all day long. With a lower BMR, you will have to eat less just to maintain your weight.
There is a lot of talk about protein in the ketogenic community. Worries about “too much protein turning into glucose” are a myth that we have discussed in detail in our book Keto as well as HERE and HERE. Getting enough protein is very important for long-term health. Maintaining lean mass as we age is very important. You don’t want to be wheelchair-bound and frail when you are older. Achieving your protein goal or going over it is very important for quality of life as we age. As we age, we need even more protein (see egg fasts section above for more).
Second, focusing only on insulin has a few issues. Many keto experts focus only on insulin and if insulin doesn’t rise, you won’t gain weight and will lose body fat. However, there is a fundamental problem with this concept. You can and will gain weight if you eat enough low-insulin foods, even just pure fat.
If this view of insulin were true, it would be impossible to gain weight by eating low to zero carbs, and that just isn’t true. I (Craig) eat primarily carnivores to manage my Lyme disease pain. I overindulged (as many of us did with COVID and other factors) last fall eating fattier meats and too much-added dairy (which is primarily fat). I gain about 20-25 pounds in a matter of months. When we got to Hawaii, I started eating lots of fish (which is naturally lower in fat) and limited dairy and I lost 20 pounds in less than 2 months. All while eating carnivore/zero carb and with fasting insulin below 5 (my fasting insulin is usually 4 or lower) and very stable blood glucose. Dietary Fat is a dial you adjust up for maintenance or gaining, down for body fat loss.
Dietary fat only has 2 places it can go. Passed right through you in the stool or absorbed into your body. This is Biology 101.
Some keto “gurus” will say that it goes right through you. This just doesn’t make any sense from a biology or evolutionary perspective. Calories were precious back in our hunter-gatherer days. If our bodies just dumped fat when we were eating a lot of it in the summer from all the animals we hunted, we would never make it through the lean winter months without stored fat. And if you flush fat through your colon in larger amounts (over 10g a day) you will live on the toilet.
Remember Olestra, the fat that went through people undigested (the infamous WOW chips) and they had to put a label on them warning of anal leakage, from an extra 10-20 grams of fat going through the stool. Studies also don’t support this idea. In THIS study there was no change in fecal output of fat when the dietary fat was 62 grams a day or 152 grams a day. It was constant and always about 8 grams a day.
Almost all the fat in your diet ends up in your bloodstream. In this case, it is either used as fuel or stored in our fat cells. Unless you are in the middle of running a marathon, the vast majority of it will be stored in your fat cells. That is just how the body works.
But this biology shows there is another very dangerous effect of too little protein when it is combined with too much fat in the diet like with a fat fast.
Almost all fat that comes in through the diet ends up in the bloodstream as chylomicrons. At this stage, they have two fates, either be used as fuel in the muscle and other tissues or be stored in our adipocytes (fat cells). Studies have shown that most of the fat first goes to our fat storage before later coming out of fat storage and used as fuel. The mobilization of fat from your fat stores to be used as fuel is called lipolysis. Eating dietary fat will shut down lipolysis quickly as the body doesn’t want an oversupply of fat in the blood.
So, what puts fat into storage? There are a couple of mechanisms. The primary controller is insulin. Yes, fat does raise insulin levels, not as much as protein or carbs, but it does raise insulin a bit. And in most people, that is enough to store it in your adipose tissue (fat cells).
Insulin does two things. It helps store fuels (fat and glucose) into the tissues. Either muscle (glycogen) or adipocytes (fat). It also acts as a net to hold back fat or glucose from being released from the fat cells or muscle. This makes sense because if you have a large amount of glucose or fat coming in through the meal, the body doesn’t want an oversupply of fuel in the blood so it stops adding fuel (stops lipolysis) and starts storing it to lower the blood fuel levels.
But there is also a lesser-known process for storing fat and that is Acylation-stimulating protein (ASP). This is a process that helps put fat into storage when insulin levels aren’t very high. However, there is a threshold level of basal or fasting insulin to enable ASP to function properly. If you have a very low basal or fasting insulin levels and eat lots of fat, the fat has trouble getting into storage where it belongs. So, the fat accumulates in the blood and results in very high triglycerides. Over time, if you continued doing this (or kept doing a fat fast, etc.) the body would scramble to find places to put the fat and it would get stored everywhere in the liver, pancreas, and other tissues, that visceral fat that is so detrimental for health. Not a good idea.
Also, important to note is the rate of uptake of these process oils. MCT oils and drinking calories enable you to drink a large amount of fat very quickly. This floods the system with energy that it struggles to deal with. In nature, we don’t have this scenario. You don’t eat pure, refined liquid fats. You eat foods like protein that contain whole fats. The whole fats you have to chew and it slows how much can be eaten in a sitting. In that way, these refined oils can be looked at as very much like processed foods. Highly refined, loaded with empty calories, and devoid of micronutrients.
So you are probably saying “But I am above my fat threshold, I still have 40 pounds to lose”. Yes, in that case, there would likely be enough basal insulin to store the fat eaten. If weight loss is your goal, storing a bunch of fat in your fat cells is not what you want to do. You want a negative fat flux (more fat coming out of adipocytes than going back in, we explain fat flux in detail in our book “Keto.” HERE). In addition to these issues, you are not getting enough protein so you are losing that precious lean mass over time. Not what we want as we age or for our BMR levels.
Third, fats are devoid of essential nutrients.
Instead of drinking a cup of fatty coffee with butter, cream, and coconut oil, I would eat a steak that gives me the satisfaction of chewing as well as nutrients to fill my body! Just look at how many nutrients you get from whole foods compared to a fatty coffee for the same 400 calories.
Other than a little vitamin A, the fatty coffee has almost zero vitamins and minerals compared to eggs and beef. It’s not even close!
Eggs and beef, provide much more vitamins, minerals, and complete proteins. It is time to ditch all the products like MCT powder, fat shots, fatty coffee, fatty lattes, and fatty drinks in general. Even if you are in maintenance. You don’t need empty calories. Stick with whole foods and all the vitamins and minerals that come with them. You will always have better long-term health by eating more nutrient-dense foods.
We are not saying to fear fats. We don’t fear fat and in maintenance consume lots of healthy fats from fatty ribeye and meats, some dairy in sauces, etc.
But when fat loss is the goal and your body is already high fat, your diet doesn’t need to be high fat. Let your body use your own stored fat for fuel instead by dialing the dietary fat down.
2. EGG FASTING
Egg fasts were quite popular for a while. But we don’t recommend them as there are a couple of issues with them.
One problem with egg fasts is that it’s really hard to get enough protein. You need about 0.8 times your lean mass in protein grams per day to maintain muscle and lean mass. For a woman that is 5 foot 4 inches and 150 pounds with 30% body fat, that is 105 pounds lean mass (150*0.7). So 0.8 times 105 is 84 grams of protein per day. This would be the goal or minimum protein needed to maintain lean mass. If you want to gain muscle, you would want more. Also, if you are over 50 years old you start needing more protein just to maintain as there is a leucine shift (leucine is the amino acid primarily responsible for stimulating muscle protein synthesis or building muscle). So you need 0.9 and 1.0 times lean mass over 50 and 60 years old just to maintain. So in general, for a typical height woman, you want closer to 90-100 grams of protein a day. Our calculator HERE factors this in automatically based on age.
Egg fasts were quite popular for a while. But we don’t recommend them as there are a couple of issues with them.
So to get a proper amount of protein a typical man would need about 24 medium-sized eggs in a day! A woman would need almost 18 medium-sized eggs to get 100 grams of protein! That is a good way to get sick of eggs quickly.
That leads to the second issue with egg fasts. You get sick of eggs quickly. I love eggs. But even with how much I love them, I would be sick of them after 1-2 days of eating 18 eggs a day.
And that is a pity because eggs are loaded with nutrients and great for your health.
Finally, the reason some people lose weight eating egg fasts is because they just get sick of eggs and undereat protein as a result. If you only eat 8-9 eggs for the day, you are only getting 40-50g of protein. This will result in losing muscle over time which can move the scale but isn’t what you want.
The most effective thing egg fasts do is make you sick of eating eggs. So instead of doing an egg fast, look into protein-sparing modified fasts (below) which will give you even better results while eating a really tasty variety of foods instead of making you sick of eating eggs.
3. EXTENDED FASTING
Extended fasts are fasts with little to no calories for longer than 24 hours. They are quite popular in several communities and with some experts.
Some extended fasting practices recommend only eating every other day. This may cause a drop in weight; however, as mentioned earlier, some of that loss will be muscle loss, not what you want.
Many times, extended fasting gurus don’t put a focus on what to eat when not fasting. As long as you don’t eat for days, you are extended fasting. Some people break their fast with unhealthy foods such as pasta or bread. This snowball of dieting will have even more detrimental effects.
Putting your body in and out of ketosis like this can result in robbing more muscle by the body wanting to use glucose, running out, and cannibalizing even more muscle before you are keto-adapted at which point muscle is preserved. Studies like THIS one have shown this including this study that showed people lose over a pound of lean mass in the first day or two of fasting, then about 1/4 pound per day after that. So if starting the fast keto, you might be able to assume you will lose 1/4 pound lean mass per day from the start (instead of over a pound at first). But even if this is true, 1/4 pound of muscle is significant.
The reason many people do extended fasting is to enter a stage of autophagy. Autophagy is when you turn over bad or damaged cells. The body takes the cells apart, removing any damage and rebuilding new cells from what is left. This can be an effective tool for people who are very sick with illnesses such as cancer, organ damage, etc. The body can in some cases turn over these bad cells and make new healthier ones. Fasting also induces more apoptosis which can be even more helpful in these cases. Apoptosis is where the body kills and removes damaged or bad cells that cannot be recycled.
But there is way too much put into autophagy from fasting gurus. It is put out there as “the fountain of youth” and you only get the benefits of it when eating nothing for long periods. This just isn’t true. First, autophagy is happening all the time are varying levels. Yoshinori Ohsumi, the Nobel prize winner for his research on autophagy, estimates that we turn over all our protein cells in our body in 2-3 months. And that is for an average person doing NO fasting! Another study estimated that up to 20% of our daily basal metabolic rate (BMR) is from autophagy.
And guess what stimulates autophagy as much if not more than fasting? Exercise and strength training! And you build muscle instead of losing it! This study showed that exercise increased autophagy in the brain and peripheral tissues. This study (and THIS one, and THIS one and many others) shows the increase in autophagy from exercise. In THIS study subjects got continuous glucose infusions while doing exercise and had greater autophagy signaling than those doing a 36-hour fast. Exercise intensity is more important than diet (fasting) for activating autophagy as THIS study shows. It states, “The most effective strategy to activate autophagy in human skeletal muscle seems to rely on exercise intensity more than diet”. I would rather eat a filet mignon for a lean protein boost and lift weights to enhance my cellular health.
Also, we store toxins in our fat cells. When we lose body fat, the toxins get released into the bloodstream. One of the primary ways these toxins get detoxed is through the stool. This is why it is so important to have a bowel movement every day, especially when losing body fat. So what happens to all these toxins when you aren’t eating anything and thus not going #2? They get reabsorbed into the body. Not healthy and can lead to the accumulation of bad estrogens (estrogen dominance) and other toxins.
Extended fasting may be a helpful tool for someone with cancer or a serious illness who wants to purge unhealthy cells; however, if weight loss is your goal, extended fasting will just result in making you weaker with less muscle mass. Less muscle mass means a lower BMR so you will need fewer calories just to maintain your weight. So as with anything, your goals are important. For fat loss, general health, or keeping disease away, eating a well-formulated ketogenic diet is what you want. Long Term Fasting isn’t needed.
4. INTERMITTENT FASTING
Breakfast isn’t the most important meal of the day … “breaking your fast” is!
I remember when I first heard about “intermittent fasting.” I thought, no, no, no. This is not good for anyone who wants to maintain their muscle. But after diving into what happens when you fast on a well-formulated keto-adapted diet, I realized that not only do you maintain your muscle, but there are other benefits as well. I now work and write early in the morning in a fasted state for about three hours and my mind has never been clearer. In this state, your ketones will likely be higher which can lead to more mental clarity.
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