Doctor here, although a Cardiologist so a bit out of my wheelhouse. Technically, it is possible to just not eat and lose all the extra weight, assuming one does not suffer from an underlying, usually endocrine, condition such as a hypo/hyperthyroid or diabetes.
Given most overweight people with a reasonable diet (doesn’t even have to be that good) have enough Vitamin stores to last close to a year before developing a serious vitamin deficiency — even water soluble vitamins such as B12 and Folate.
Therefore, it is physiologically possible to not eat for very long stretches at a time. Is it healthy? No. Potentially dangerous? Absolutely.
The first 2 weeks to a month are possibly the most dangerous, as your body depletes the readily accessible carbohydrates, and instead starts breaking fat down and using that as energy, creating ketones as byproducts.
This is the basis of the fad keto diet. Eat only fat, use only fat. The thing with the keto diet however is that almost all food contains some carbohydrates, no keto diet will give you a ketosis as severe as starvation ketosis.
Contrary to popular belief, ketosis is not good for you. Ketoacidosis kills diabetics all the time. Ketones are very acidic compounds, your body uses up basic compounds in an attempt to neutralize ketones and bring your blood pH to a more reasonable level quite quickly. Ketones also require a large amount of water to excrete, easily causing dehydration.
Most tissues, especially the brain, prefer carbohydrates to fat as energy. Your skeletal muscle starts to function inefficiently, and starts to produce lactic acid, further dropping the pH of your blood, exacerbating acidemia.
When you are overweight, your exocrine glands (think of them as the digestion juice glands) are hyperplastic (more cells than normal) because your body has adapted to processing more food than necessary. This can lead to over excretion of, again, acid.
There is always a chance that all the cholesterol you’ve built up over the years of overeating, now concentrates in the gallbladder as you stop eating. This can lead to gallstones, which can easily obstruct the ducts that the pancreas uses to send juices out. The juices in the pancreas are designed to dissolve organic substances. Our body is made up of the same stuff that food is made up of. If obstructed, the juices will be released into the pancreas and essentially dissolve it. This is pancreatitis — a life threatening condition.
Your stomach is used to excreting similar juices. If there is no food to soak up this juice, it can burn holes into your stomach or the first part of your gut, called the duodenum. This is how ulcers form, and ulcers like to bleed — another life threatening condition.
The exocrine (juice) part of digestion corrects itself quite fast, maybe 2 weeks of starvation. If your pancreas and GIT mucosa withstand the imbalance, most of the acutely life threatening conditions of starvation have been averted.
Your endocrine (the longer acting, more global part of your regulatory system, if you will) takes longer to adjust, hormones like Ghrelin Leptin etc.. Maybe a month into starvation you will stop feeling hungry altogether.
A month on only water and your body will adjust into a state of hibernation, using up energy for only the most vital organ functions. It will be operating at maybe 10% of normal capacity, and you will definitely feel like you’re 10% alive. Getting up to go to the toilet will feel like running a marathon, processing stimuli such as watching TV for 10 seconds will feel like sitting an 8 hour exam.
Possibly the most dangerous part of starvation however, is starting to eat again. Depending on how long you’ve been starved, your body won’t know what to do with all this food anymore. When you are starving, the process is rather slow happening over weeks to months. Eating a cheeseburger after a 6 month starvation period is a process that could kill you in 30 minutes.
Pancreas will freak out and release everything it’s got, against likely leading to its own auto-digestion.
Your blood pH might be around 7. Normally pH is about 7.45, pH is logarithmic scale therefore 7 is 4.5x more acidic than 7.45. This overcorrection can lead to a whole host of issues, including respiratory arrest.
Hope this surface scratcher explained it a little bit. Nutrition and Endocrinology is a very complex topic (too much for us heart plumbers), and there is still so much we do not know about nutrition, especially the role of gut bacteria in the body’s regulation.
Edit: This wasn’t meant to be a keto diet bashing post. I was bored on a train and decided to elaborate on a topic I saw on my phone. I don’t keep up with endocrinology journals or nutrition journals. As a Cardiologist, I can say I wouldn’t recommend keto diet to any of my patients, strictly from a cardiology point of view. Please take the statements I have made with a grain of salt! Doctors are not encyclopedias of peer reviewed meta analysis! That’s why we have a lot of specialists.
You can last weeks without eating, just not without water
I don’t know if they teach about the Holocaust in school anymore but when I was a teen we had textbooks with pictures of what happens when people’s fat stores get used up
Fat IS energy, and is good for feeding the most essential energy. It’s why it’s nearly impossible and horribly unhealthy to be below. 6-8% body fat, your body would literally be eating itself between meals.
Although ENERGY isn’t everything that’s required for your body to function, and you need tons of other nutrients as well. Proteins, calcium , iron, etc are all required to maintain bodily function. Without them, you will die.
Think of it like this. Your body is a car, and fat in this analogy is gasoline. Obviously the bigger the gas tank Theo get you can go between fillups. What happens when you need new brakes? Change your oil? Tires? Obviously the car needs the gas to go, but so much more goes into keeping the car moving than just gasoline
Spouse recently died of esophageal cancer. He went through daily radiation, and weekly chemotherapy over a seven week period starting a year ago next week. This pretty much killed his ability to swallow. As frustrating as that is, he swore he never felt hungry. He was trying to consume anything with calories, and kept losing weight. The doctors, and there were many, would always have their nurses ask, “Have you had any unexplained weight loss?”
Um, technically, no. “He’s lost lots of weight, but we know why, so its not unexplained?!?!”
He lost 50 pounds (185 to 135) before they got him scheduled for surgery. They went in and figured out that they couldn’t get an endoscope down his throat (“Well, duh, doc! I could have told you that! In fact, we’ve been telling everyone!!”) They opened him up and found that cancer had progressed too far for the surgery, so they closed him up again. The next day, they put in a feeding tube.
With the feeding tube, he gained back up to 155 pounds. He couldn’t swallow his own spit, violently coughing up mucus and spitting it into a cup.
So yes. You can lose weight by simply not eating. I don’t recommend it.