I call fasting ‘The Ancient Secret of Weight Loss’ because it is one of the most powerful dietary interventions for weight loss, yet it has been almost completely ignored it in recent years.
Is there a maximum number of days to fast? No, not really. However, I will add a cautionary note. If you are taking medications or especially if you have diabetes, you need to discuss this with your physician before starting. The blood sugars often come down with fasting regimens, but if you are taking medications, it may come down too low. This is a potentially fatal condition called hypoglycaemia. It often manifests as shaking, sweating and sometimes seizures. Medications often need to be adjusted including blood sugar and blood pressure medications.
Also, if you feel unwell at any point during the fasting, you must stop. You may feel hungry, but you should not feel faint, or unwell or nauseated. This is not normal and you should not attempt to ‘push through’. I am not specifically recommending any fasting regimens, only trying to document various fasting regimens in widespread use.
The world record for fasting is 382 days. This 27 year old Scottish man fasted for weight loss as he weighed 456 pounds at the start. During this time, he only took a multi-vitamin, and something called ‘Paladac’ which was vitamin C and yeast. Why on earth anybody decided that eating yeast was that important is really quite beyond me, but hey, this was 1973, when pet rocks and disco was popular, too, so there you go. By the end, he weighed 180 pounds, and remained stable for five years, at which he was only 196 pounds.
He drank unlimited non-caloric fluids to prevent significant dehydration. At various periods, he did receive some potassium and sodium supplements, but not regularly and he was monitored by a physician throughout the fasting period to see if there was any deleterious effects on his health.
Constipation is one of the main problems we see in fasting. The reason seems simple enough. There is very little going in the mouth, so little comes out the other end. This is a problem we face routinely in our IDM clinic.
With this world record fast, this patient had bowel movements roughly every 37-48 days. What’s important to note is that this is a normal phenomenon. You do not need to have a daily bowel movement to feel well. People only have discomfort if there is a lot of stool that does not come out. With fasting, there is not a lot of stool inside the intestines, so not a lot needs to come out.
Nevertheless, less than once a month seems kind of extreme. We will often recommend standard laxatives such as milk of magnesia, available over the counter in Canada.
Fasting and electrolytes
The accompanying graph shows that blood sugars do go lower, but remain at the lower limit of normal, without any symptomatic episodes of hypoglycaemia. This is, of course, to be expected, since the body will begin the process of gluconeogenesis (making of new glucose) in order to supply the brain and certain other parts that need glucose (renal medulla and red blood cells). Even the brain is mostly using ketones at this point.
As previously shown, very little muscle is consumed to provide glucose (gluconeogenesis). Instead, the glycerol backbone from triglycerides (fat) is recycled into glucose while the three fatty acid chains are used for fuel by most of the body.
Calcium and phosphorus levels in the blood vary over the fasting duration but generally remain within the normal limits and are virtually unchanged by the end of the fast. The same goes for plasma urea and creatinine, which are widely used measures of kidney function. Sodium, potassium, chloride and bicarbonate were all unchanged and in the normal range. In this study, uric acid remains stable although other studies have shown some increased uric acid.
Serum magnesium levels did decrease in this study. This is consistent with what we see clinically in our clinic as well. It seems to be especially prevalent in diabetics. 99% of the body’s magnesium is intracellular and not measured by blood levels. In this study, researchers took the extra step of measuring the magnesium content within the cells and the erythrocyte Mg levels remained firmly in the normal range. Nevertheless, we often supplement with magnesium to be on the safe side. Epsom salt baths are good for this.
The rate of weight loss was 0.72 pounds per day averaged over the entire 382 days. Other studies of fasting over 200 days had shown similar rates of weight loss (from 0.41 to 0.67 pounds per day) for periods of 210, 236, 249 and 256 days. This average of 0.565 ((0.41 + 0.72)/2) is actually quite interesting.
We assume that one pound of fat is 3500 calories. This is a widely quoted figure, but not especially accurate. If we assume that one eats 2000 calories per day, then we would expect 2000/3500 = 0.57 pounds weight loss per day, which is fairly close to that number actually seen.
So, for a patient with 100 pounds of fat to lose, you might expect that it would take roughly 200 days to lose it all. 200 days! This assumes that Caloric Expenditure remains stable with fasting, which seems to hold true. In other words – metabolism does not decrease in fasting. A prolonged caloric reduction, on the other hand, is shown to decrease metabolism.
The ancient secret
I’ve sometimes called Intermittent Fasting the ‘Ancient Secret’ of weight loss. Why do I resort to such hyperbole? Well, because it’s true. It is an ancient technique of weight loss – dating at to the time of the ancient Greeks over 2000 years ago.
So, if you want to talk about time-tested practices, nothing beats fasting. Consider that low-carb diets such as endorsed by William Banting also have a long history but only dating from the mid 1800’s. Obesity was quite rare in the time of Jesus Christ (another strong proponent of fasting, 2017 years ago). The calorie-reduced, low-fat diet, on the other hand has a history of only about 50 years, and a perfect treatment record, unblemished by success.
But why is fasting a ‘secret’? Well, because the nutritional authorities have spent the last 30 years convincing us that we need to eat more to lose weight. We’ve all heard these lies:
- You must always eat breakfast within one minute of getting out of bed.
- You must eat meals and snacks constantly, all day long or else you’ll be consumed by hunger and stuff your face with Krispy Kreme donuts.
- You should eat a bedtime snack or else you’ll be hungry while asleep and then stuff your face with Krispy Kreme donuts when you wake up.
- You must never, ever miss a meal, otherwise you’ll be consumed by hunger and stuff your face with Krispy Kreme donut.
- If you miss a single meal, you’ll develop eating disorders like anorexia nervosa.
Fasting does not cause anorexia
Fasting is not, like, exactly fun. It’s a hell of a long way from morbid obesity to anorexia. Furthermore, anorexia is a psychologic disorder of body image. Fasting does not lead to anorexia any more than washing your hands leads to obsessive compulsive disorder. But these fears persist.
Nevertheless, because of all the worries, you can rest assured that there are studies that show that intermittent fasting does not lead to eating disorders.
Sadly, the public at large has bought into these lies. You can see that from 1977, the vast majority of people ate 3 times a day. By 2003, most people were eating 5-6 times per day. Eat more to lose weight? This weight loss advice is about as useful as a third nostril.
Much of this nonsense is funded by Big Food and Big Soda. They want to sell more food. It’s easier to sell more food if people are eating more frequently. So, in order to do that, they needed to make sure that you didn’t ever miss a single meal.
So here’s the bottom line.
Can you fast? Yes – literally millions of people around the world for thousands of years have done it.
Is it unhealthy? No. In fact, it has enormous health benefits, that we have not even touched upon yet.
Will you lose weight? Here is the crazy thing. People have been convinced that fasting will make them gain weight (the bogeyman – starvation mode). OK, Einstein – if you don’t eat anything for 2 weeks, do you think you will lose weight? Of course.
Is it difficult? Not really. Millions of people do it. But it’s not exactly fun, either.
So fasting is effective, simple (one main rule – don’t eat), flexible (lots of different regimens), practical (saves time and money), and virtually guaranteed to work. So why don’t people support it? Because nobody makes money when you fast. Only when you buy crazy unnecessary things like meal replacement shakes.
You can lose weight and get healthy for free? Nobody must learn this Ancient Secret of Weight Loss!
Top videos about fasting
Earlier with Dr. Jason Fung
More with Dr. Fung
His book The Obesity Code is available on Amazon.
His new book, The Complete Guide to Fasting is also available on Amazon.