- A fast is the fastest way to lose weight. Many people already naturally fast for certain periods due to religious or cultural reasons.
- Intermittent fasting, a form of partial fasting, has recently become popular as a dietary method for maintaining a good physique, but is no magic bullet.
- Juice cleanses are essentially just a fast by another name - and not a very smart one.
- The protein sparing modified fast is a diet designed to help alleviate the inherent problems of a fast, making it a smarter crash diet.
- At the same time, crash diets are not for everybody, and still carry risks. Thus, you should be aware of these risks and carefully consider your options. Usually, slower diets are more sustainable and healthy.
The human body is made up of, and fueled by, matter - in the form of organic compounds that we eat in our everyday meals. Food is broken down into calories, which are then used in metabolic processes to generate energy. It’s well established in the scientific literature that the calories in, calories out (CICO) model is currently the most accurate method for understanding how people gain or lose weight.
Under this model, we burn a certain number of calories per day, and eat a certain number of calories per day - when we burn more than we eat, the difference has to be made up by breaking down stored tissue, leading to weight loss, and when we burn less than we eat, the excess is stored as excess tissue for later usage.
Of course, CICO isn’t a perfect descriptor for what’s going on, because there’s a lot of complications involved. Our metabolism isn’t set, and changes regularly, so it’s hard to tell exactly how much we’re burning. Further, most people don’t track their dietary patterns with any degree of accuracy, so it’s hard to know how much we’re consuming either. All the numbers are very fuzzy.
One thing is certain: under the CICO model, there are limitations on how quickly we can gain or lose weight. In particular, the absolute fastest that we can lose weight is simply by eating precisely 0 calories per day - which is typically called, well, a fast.
Fasting is an established practice in many cultures. It's also a natural part of our day: we call the first meal of the day “breakfast” because we’re breaking the nightly fast that occurs while we sleep. People may fast for small periods naturally due to lack of food available, long periods of sleep, inability to eat during periods of sickness, or as part of religious or social rituals.
One of the most well-known and prominent fasts is the Muslim practice of Sawm during Ramadan, in which Muslims are required to fast between sunup and sundown for the month. While they’re allowed to eat and drink as normal after dark, they may not do so at all during the daylight.
One recently popular diet strategy is that of "intermittent fasting", which mimics the Muslim fast. In intermittent fasting, you are able to eat only during a small window (usually the last 8 hours of the day or so), and are only allowed to drink zero calorie drinks or take a bit of supplementation during the day.
In recent years, intermittent fasting has become a fad in the fitness industry as a way of promoting weight loss and improving leanness. While there have been many potential benefits advanced by proponents, the science has generally confirmed that intermittent fasting is no magic bullet - we still have to follow the general rules proposed by the CICO model.
Intermittent fasting may help with adherence, since you get more psychologically used to the idea of not eating for a large portion of the day, and since the limited amount of time you have to eat may make it easier to limit your overall calories.
Fasting like this may have positive effects on body composition and weight, but must be distinguished from a complete fast, which is the kind that actually causes the fastest weight loss. In a complete fast, you would eat 0 calories per day. Depending on your metabolism, this would result in a rate of weight loss of about 1lb per day or two.
Naturally, this is pretty rapid! The typical recommendation is to aim for a deficit of no more than 500-1000cal/day, but a total fast would be more on the lines of a 1500-2500 deficit. A huge deficit like this will obviously cause issues - massive hunger, loss of muscle mass due to lack of protein, low energy levels due to lack of carbs, hormonal issues due to lack of fats, potential long term health/metabolic issues, poor recovery and increased risk of injury, psychological distress, and more. It's just not a good idea in the slightest.
Juice Cleanses - Fasting By Another Name
It’s become fashionable in recent years to undergo “juice cleanses”. These cleanses are supposed to clear the body of (undefined, nebulous) “toxins” with an all liquid diet, typically made up of low-calorie juiced vegetables. There’s a lot of reasons why these diets aren’t a good idea, but at the very least they don’t usually pitch themselves as long term solutions, instead being intended as a short term kick to your system.
These juice cleanses are extremely similar to a fast due to their low calorie content. They claim to be a better solution because of the high levels of “nutrients” contained in the juices, but this ignores the fact that calories themselves are the most important nutrients, their macro forms (fats, carbs, protein) have important metabolic benefits, the process of juicing removes valuable fibers, and no amount of micronutrients will make up for the fact that you're basically starving yourself. Juice cleanses are not “healthy”, but are instead just fasting under a different name.
Not to mention that typically, cleanse providers will charge you a pretty penny for their proprietary blends of juices and whatnot. The only thing a cleanse will clean out, in the end, is your wallet!
Working Around The Problem Of Fasting
In many cases, it is possible to fast while actually alleviating some of its damaging and difficult features. One of the biggest problems with fasting, aside from the psychological difficulty, is the possibility of muscle loss.
When in a carb burning state (the standard state most of us are in at any point), your body needs carbs to fuel itself. In the absence of carbohydrate, it will switch over to an alternate metabolic state (ketosis) in which fat is burned more readily for energy. However, because this takes some time, the body can run out of carbs and start searching for alternate sources of them - breaking down muscle tissue in the process - before it fully switches over to ketosis.
Thus, before starting a fast it can help to kickstart the process early, by intentionally going into ketosis ahead of time. This occurs only in the absence of carbs, so you need to eat a diet where your primary calorie source is fats, and with a moderate amount of protein and virtually no carbs. Doing so and then transitioning from ketosis into a fast is a bit easier than going directly for the fast, and results in less initial muscle loss.
However, muscle loss during a fast also occurs in an ongoing fashion, due to the lack of protein. Protein is necessary to maintain muscle protein synthesis, the process that is constantly responsible for building muscle in the body. With compromised muscle protein synthesis, you can lose muscle mass pretty quickly. This isn’t ideal, since you’ll lose strength and your metabolism will decrease even more than it should.
As a result, the protein sparing modified fast (PSMF) was designed. The intent of this diet was essentially to be a fast, but to add in the necessary amount of protein to prevent muscle loss. Typically, about 0.82g/lb of bodyweight/day is the recommended target. For example, I weigh about 200lbs, so this comes out to 164g/day of protein. Protein has 4 calories per gram, so this means I’d be eating only about 656cal/day, plus some trace fat calories from my protein sources - typically around 800cal/day total.
A PSMF approach typically focuses only on very lean proteins plus some supplementation designed to help prevent nutrient deficiencies. The typical recommendation is to supplement with a multivitamin, and be sure that you're getting supplemental potassium, magnesium, sodium, and calcium, as well as a fish oil supplement.
Some light weight training is also recommended to help maintain muscle mass. Obviously, this means you'd lose weight a bit slower than a full fast - but you'd also be avoiding many of the potential downsides of a full fast, including the intense hunger and muscle loss. Even then, it’s probably not a great idea to stick with it for a very long term.
PSMF’s are used for extreme weight loss, and are sometimes used by bodybuilders and other competitors looking to quickly prepare for a competition. However, PSMF still carries health risks, and it would always be a better idea to stick to a less restrictive diet plan and simply plan a bit more in advance than to crash diet at the last minute.
Is There A Place For Crash Diets?
One benefit of crash diets is that since they don’t last as long, it’s “easier” for people to get into them. You follow a strict plan, there's not as much thought or effort to it, and you see results.
At the same time, the short term nature of these diets often means long term weight regain, since the structure of such a diet is so restricting that it’s hard to stick to, both psychologically and physically, in the long term. As a result, many people fail to establish the good long term diet habits that are necessary for long term success. Good habits are a process that take time and can't always be learned with a crash diet.
This doesn’t mean that they’re useless. Crash diets like this can be useful for the achievement of short term goals, as in the example of bodybuilders preparing for competition. They can still be useful so long as you fully understand the purpose and risks of such a diet.
Diets like a complete fast, and even a modified version like PSMF, still carry risks due to their extreme nature. It may be the fastest that you can safely lose weight, but this doesn’t mean that it’s always the best strategy. Instead, taking a more reasonable, long term approach is often the key to success. Otherwise, you tend to get trapped in an endless cycle of yo-yo dieting which is clearly unhealthy.
Have a plan, know the risks, and approach your dietary plan appropriately. I don’t recommend such a diet if the goal is long term health alone.
- Understanding Your Actual Metabolism
- Programming Your Macros Part 1: General Health and Wellness
- Programming Your Macros Part 2: Gaining Muscle
- Programming Your Macros Part 3: Weight Cutting and Weight Loss
- The Dangers of Clean Eating (And Other Food Babe Related Things)
Are you interested in perfecting your deadlift and building legendary strength and muscle? Check out my free ebook, Deadlift Every Day. Or maybe a well-rounded beginners program for those looking to build strength, muscle, and endurance? Check out my other free ebook, GAINS.