by Nils Osmar. June 3, 2022
Water fasting has been found to extend the lifespan in animals. In fact, it’s one of the gold standards by which other approaches to life extension are judged.
It’s been clearly associated in a number of different life forms, ranging from yeast to insects to mammals. with an increase in longevity, and with improvement in numerous health markers. See article: Intermittent fasting makes fruit flies live longer — will it work for people?
Has fasting been proven to extend the human lifespan?
No. But it’s unlikely that anything ever will be, because it would take longer than the typical human lifespan to establish whether a particular intervention has really extended life in humans. Unless we want to wait a few hundred years for definitive evidence, animal studies are our best guide at the moment.
It is interesting that both fasting and CR (caloric restriction) have been shown to extend the lifespan significantly in both sexes in our close cousins, rhesus monkeys. This gives weight to the notion that it may have the same benefits in people. See article: Caloric restriction improves health and survival of rhesus monkeys.
In addition to life extension (in animals), the Johns Hopkins Medicine website lists several possible benefits to fasting, including potential improvements in:
- Thinking and memory. “(Fasting) boosts working memory in animals and verbal memory in adult humans.”
- Heart health. “(Fasting) improved blood pressure and resting heart rates as well as other heart-related measurements.”
- Physical performance. “Young men who fasted for 16 hours showed fat loss while maintaining muscle mass. Mice who were fed on alternate days showed better endurance…”
- Diabetes and obesity. “…Obese adult humans lost weight through intermittent fasting.”
- Results of surgery. “In animals, intermittent fasting reduced tissue damage in surgery and improved results.”
Is it all about calories?
Some studies suggest that most of the benefits of fasting (including its life-extending qualities) come from the fact that if we fast. For example, if we skip eating one or two days a week, our total intake of calories during that week will be lower.
Other studies suggest, though, that taking a total break from food for a stretch of time has benefits unrelated to caloric restriction. One advantage for some people is that, once we get used to going for a few hours or days without food, doing an occasional fast can be easier than constantly restricting our calories, because we’re free to eat whatever we want when we’re not fasting. So instead of constantly counting calories, we only need to think about our caloric intake on our fasting days.
Types of fasting
Most people just drink water when they’re fasting. If this works for you, that’s great. But there are fasts that include a few other ingredients.
A “fast” is defined as abstaining from “all or some kinds of food or drink.” This gives a bit of leeway for people to experiment and find an approach that works for them.
Some common types include:
- Dry fasting, in which the person doesn’t eat or drink anything (including water). Some “dry fasters” even avoid taking showers or baths when fasting. I personally don’t do and don’t recommend dry fasting (for more than a few hours) unless it’s being done under close medical supervision. It’s been associated with a risk of kidney stones, seizures, low blood volume and low blood pressure and even the possibility of death.
- Water fasting, which sometimes includes coffee or tea (but no caloric food or liquids). According to this this study, water fasting can be safe and beneficial if done correctly. However, there can sometimes be negative effects. “After 8 days of WF, all subjects were found to remain safe and feel the sense of well-being. However, the appearance of the above-mentioned adverse metabolic effects, despite partially effective renal compensations, suggests that the further continuation of fasting intervention by the subjects would be detrimental to their body.” If you do water fasting, I’d recommend reading up on both its possible benefits and possible dangers first, so that you can approach it as safely as possible.
- Fat fasts (in which one eats only fats)
- Protein fasts (in which one eats everything except protein). (The terms can be a little confusing!)
- Fasting Mimicking Diets, in which the person eats somewhere in the range of 750 calories a day, keeping protein and carbohydrates low (but only for a three to five day stretch; FMDs are not meant to be permanent diets).
- Juice fasts (in which one drinks only juices). The quality of a juice fast can very greatly depending on what types of juices are being consumed. A fast in which you drink only celery and parsley juice would be expected to have a very different effect on the body than one in which you drink high glycemic juices such as apple juice, orange juice or watermelon juice, which could cause blood sugar and insulin to spike.
- One benefit of low-carb, low-glycemic juice fasts over water fasts is that they may help us to avoid developing micronutrient deficiencies associated with the lack of nutrients coming into our bodies during a fast.
I’ve done several water fasts (water plus electrolytes) over the past few years and have generally liked them and benefited from them. I’ve lost body fat, my cholesterol and triglycerides have improved, and my A1C has dropped significantly after fasting. There’ve been no negative side effects that I’m aware of, although it’s possible that I may have lost some muscle along with the body fat. But if so, I regained it when I resumed feasting. So I plan to do more fasting in the future.
I also sometimes do fasting mimicking diets that last up to five days, and bouts of Low Carb Juice Fasting (LCJF), in which I drink (mainly) water but might also drink two or three glasses of very low carb juice – either a juice I’ve made myself, or a low carb prepackaged juice that fits my specs.
I’ve based some LCJF fasting around a juice made by Suja called Uber Greens. It costs in the range of $10 for a 46 ounce bottle. It’s organic, cold pressed, and pressure pasteurized (which leaves more enzymes intact than heat). The ingredients include celery, cucumber, collard greens, lemon, kale, green chard, parsley, ginger, and romaine lettuce. An 8 ounce glass has only 7 grams of carbs and 1 gram of protein. There are almost six glasses in a bottle.
I have an Omega masticating juicer which is highly rated for separating the liquid from the pulp without harming the nutrients in the juice. One favorite juice is made from celery, cucumbers, parsley, tomatoes, and a carrot or two. For salt, I add a little RealSalt, a brand of natural, unprocessed salt which does not have the micro-plastics which have been found in sea salts.
But aren’t juices high in carbs?
Some are. I’d never base a juice fast around drinking apple juice, orange juice, or other high carb, high glycemic juices. (I tried once, decades ago, and my blood sugar shot through the roof.) The carbohydrates in fruit have been found to raise blood glucose and to spike insulin and mTOR, the opposite of what most people want when fasting.
What I mean by low-carb, low-glycemic juice fasting is drinking things like cucumber juice, parsley juice, and fermented pickle juice and/or sauerkraut juice (and also lots of water, and some electrolytes).
The reason I (sometimes) do low carb juice fasting is because it’s a way of including some micronutrients such as enzymes, vitamins, minerals, and phytonutrients while fasting. I mentioned micronutrient deficiencies above; they become more of a problem as we age because of a reduced ability to absorb nutrients. I’m 69 at the time of writing this, so have become aware of this as a possible issue for myself when fasting.
I’ve found that low carb juice fasting can be just as effective as water fasting for my goals (keeping my weight down around where I like it, and promoting general health, ketosis and autophagy).
Are low carb, low-glycemic juice fasts better than water fasting?
Not necessarily, though some may find them easier to do (and be able to fast longer as a result).
Water fasting is still considered the gold standard though, and may have some advantages over fasts that provide some nutrients. One is that it gives us a total break from food allergies and sensitivities. It’s important, though, to take electrolytes when water fasting. Don’t drink purified/distilled water during a water fast without adding electrolytes in.
Another alternative to water fasting is to drink fasting-mimicking smoothies (made from avocados, tomatoes and a few other ingredients. But don’t add protein powders. Like l0w-carb juice fasts, fasting-mimicking smoothies provide micronutrients and electrolytes. More information
Who shouldn’t fast?
According to the Johns Hopkins website, people in these groups should not fast:
- Children and teens under age 18.
- Women who are pregnant or breastfeeding.
- People with diabetes or blood sugar problems.
- Those with a history of eating disorders.
The author advises that “before you try intermittent fasting (or any diet), you should check in with your primary care practitioner first.”