Is Juice Fasting Keto? The Do’s and Don’ts of a Juice Fast
You’ve probably heard the buzz on juice fasts. These juice-only cleanses are said to help with weight loss, detox, and nutrient status.
Getting started is easy. You just need a high-quality juicer and organic produce, such as raw fruit and leafy green vegetables.
But before you run to the store, there are some things you should know about juice fasting. Yes, there may be some health benefits associated with this practice, but not eating solid foods for an extended period comes with legitimate safety concerns.
In this article, you’ll learn everything you need to know about juice fasting: potential benefits, risks, fruit juice vs. vegetable juice, and how to structure your own juice cleanse.
When you fast with juice, you consume only fruit and vegetable juice for a set period of time. People typically start with a three-day juice fast, but some go weeks drinking only juice.
There are many reasons to do a juice fast. Some people do it to lose weight while others do it to consume more nutrients, feel better, or to detox from toxins. Some of these reasons have evidence behind them, while others (like detoxification) do not.
To make your juice, you process organic fruits and vegetables in a juicer every day. This removes the plant matter (mostly fiber), leaving behind mineral-rich liquid.
Juice fasting involves calorie restriction, but it’s not the zero-calorie fasting typical of most intermittent fasting programs. That’s because during a juice fast, you consume calories — mostly in the form of sugar — from fruits and vegetables.
Due to its high sugar content, fruit juice is higher in calories than vegetable juice. (Vegetable juice is a more metabolically-friendly option, but more on this later.)
On many juice fasting regimens, you can also drink herbal teas and smoothies alongside your fresh juice and filtered water. Some protocols also include “detox” supplements alleged to help remove toxins from your body.
Different people will fast with juices for different reasons. One person might do it for weight loss, another to boost their nutrient intake, and another still for detox.
Does Juice Fasting Help You Lose Weight?
There is some evidence that juice fasting promotes weight loss. This effect is probably due to a lower caloric intake during these temporary cleanses — fewer calories equals less weight gained.
For example, in one small study, 20 healthy adults lost significant weight after consuming only fruit and vegetable juices for three days[*].
And as for nutrition — yes, it’s true that fruits and vegetables are rich sources of vitamins, minerals, and antioxidants. A fresh blend of kale, spinach, and ginger yields an impressive array of nutrients that puts the Standard American Diet to shame.
Does Juice Fasting Detoxify the Body?
Many people are convinced that juice fasting helps clear toxins from the body.
Unfortunately, there isn’t any evidence for this widespread myth.
The liver, for example, is an organ that helps your body package toxins for excretion in urine or feces[*]. Because the liver aids in detoxification, many claim that you need a liver detox — a juice cleanse, for example — from time to time.
But this doesn’t make sense, because your liver doesn’t store toxins. There are no toxins to detox.
The term juice cleansing, then, is misleading. You might be drinking valuable minerals, but no organs or toxins are being cleansed.
Further evidence against detox diets comes from the National Center for Complementary and Integrative Health, a division of NIH.
“Diets that severely restrict calories or the types of food you eat usually don’t lead to lasting weight loss and may not provide all the nutrients you need,” they write[*].
That said, there may be some non-detox benefits related to juice fasting.
There isn’t an abundance of research on the health benefits of a juice fast. Nonetheless, there are a few small studies suggesting the practice might be beneficial.
With that in mind, here are four potential benefits from juice fasting.
#1: Weight Loss
In the previously mentioned study, 20 healthy people lost significant weight after a three-day juice fast[*].
One reason why? They ate fewer calories. Eating fewer calories (or fasting) is a proven way to lose weight.
These same researchers, interestingly enough, found another potential factor driving juice-fasting-related weight loss: gut bacteria.
Those who completed a juice fast shifted their gut microbiomes. These shifts were towards bacteria linked to weight loss.
However, understand that initial weight loss during a fast is often water weight[*]. This water is shed from glycogen stores (stored glucose), which are used up during fasting and carb restriction.
Sustainable fat loss, on the other hand, happens when you fat-adapt on a ketogenic diet, intermittent fasting protocol, or some combination.
#2: Heart Health
While it’s too early to claim juice fasts as heart-healthy, there are two small studies worth mentioning.
The first was the aforementioned weight loss study[*]. After three days of juice-only dieting, 20 healthy people had:
- Significantly higher levels of nitric oxide (NO), a blood-vessel-relaxing chemical linked to a healthy-functioning cardiovascular system[*].
- Significantly less lipid oxidation. Oxidized lipids accelerate the progression of atherosclerosis, or the buildup of plaque in the arteries that’s the primary feature of heart disease[*].
In another small study, researchers put five healthy males on a juice fasting regimen of 150-300 calories per day. After eight days on this protocol, the men had:
- Lower triglycerides
- Lower insulin levels
- Higher low-density lipoprotein (LDL) concentrations
The first two bullets are considered positive for reducing heart disease risk, while the last bullet (higher LDL) is not.
Higher concentrations of LDL have been linked to increased risk of heart disease. In fact, there’s abundant evidence that LDL particles are causative in the progression of atherosclerosis[*].
#3: Vitamins and Minerals
Fruits and vegetables are some of the most nutrient-dense foods on the planet. Fortunately, most of these vitamins and minerals are conserved after juicing.
Here’s a sampling of vitamins and minerals (and their functions) you’ll find in commonly juiced plant-material.
- Vitamin C: Supports immunity, antioxidant defense, and collagen production. Vitamin C is found in spinach, broccoli, kale, cherries, oranges, and papayas[*].
- Vitamin A (beta carotene): Serves as an antioxidant and converts to preformed vitamin A (retinol) in your body to support immune and bone health[*]. It’s found in carrots, spinach, and pumpkins.
- Folate (vitamin B9): Crucial for cellular energy production and DNA synthesis. It’s found in broccoli, spinach, and lettuce[*].
- Magnesium: Essential for muscle function, energy production, and blood sugar regulation[*]. It’s found in spinach, kale, chard, and bananas.
- Calcium: Necessary to structure your bones and teeth, contract your muscles, and much more. It’s found in spinach and cruciferous vegetables[*].
Over millions of years, plants have evolved special compounds to keep insects and other predators away. These compounds are antioxidants (or polyphenols), and they’re mildly toxic to the animals that eat them.
When humans eat polyphenols, it activates a stress response. “Oh, here’s a bit of poison,” says the stress response, then, “Let’s ramp up our defenses!”
In other words, plant-based polyphenols put your body in cleanup mode. You start making internal antioxidants (like glutathione), and you end up healthier than when you started[*].
That’s how potent antioxidants — like sulforaphane from cruciferous vegetables — work[*]. They don’t nourish your cells per se, but rather activate health-promoting processes.
And if you’re doing a proper juice fast, you’re eating many plant polyphenols: flavonoids, flavanols, anthocyanins, and carotenoids. Researchers believe these compounds likely drive any cardiovascular benefits linked to juice fasting[*].
You’ve read the good news on juice-only fasting. Now for the not-so-good news: the safety concerns.
The truth is, there are reasons to be careful with this type of fasting, especially for an extended time. A juice fast is not part of a healthy lifestyle, and should be kept to a short period (i.e., less than one week).
The most immediate safety concern is contamination. Fresh, unpasteurized juice doesn’t stay bacteria-free for long — and certain bacteria, if ingested, can make you quite sick.
For this reason, the NIH recommends that children, elderly people, and those with weakened immune systems be cautious with juicing[*].
Another safety concern involves oxalates. Oxalates are compounds found in green leafy vegetables like spinach. In excess, oxalates can burden your kidneys.
In the context of a normal diet, oxalates are usually not a problem. But if you’re juicing a lot of spinach, chard, or other green leafy veggies, you should consider monitoring your kidney function.
At least one case of nephrotoxicity (kidney toxicity) associated with juicing has been reported in the American Journal of Medicine[*]. To be clear, this particular juice fast lasted for six weeks, which is longer than your average cleanse.
Also, if you’re using copious amounts of raw kale in your juice, it could be affecting your thyroid gland. Compounds called goitrogens in cruciferous vegetables may interfere with the action and absorption of your thyroid hormone, especially when iodine status is low[*].
It’s unclear just how much kale or kale juice you’d have to consume to notice negative effects. Talk to your doctor if you have thyroid issues.
Finally, juice-only fasting is a form of calorie restriction (CR), and not everyone responds to CR favorably. If you experience persistent headaches or other bad side effects, listen to your body and back off.
It depends on your individual situation and how you structure the fast.
For one, juicing removes the fiber from whole fruits and vegetables. For those with gut issues, this can be beneficial, as too much fiber can irritate the gut lining and exacerbate small intestinal bacterial overgrowth (SIBO).
But for others, cutting out fiber could be a bad move. After all, dietary fiber has been shown to support digestion, improve heart health, curb cravings, and feed beneficial bacteria in the non-compromised gut[*].
Then there’s protein and fat. You don’t consume either of these crucial macronutrients while fasting on juice.
In the short term, this is probably OK. Fasting helps you lose weight and activate cellular repair mechanisms like autophagy.
But longer term, protein restriction will result in the loss of lean mass. Losing muscle is not, in most cases, a sign of improving health.
Dietary fat is nearly as important as dietary protein. For instance, eating fat helps you absorb fat-soluble vitamins like A, D, E, and K[*].
You can drink all the vitamins you want during a juice cleanse, but if you don’t absorb them, what’s the point?
When it comes to your health, the type of juice — fruit or vegetable — also matters.
If you’re on a keto diet, for instance, even moderate portions of carbohydrates — say, 20 grams — could raise your blood sugar enough to kick you out of ketosis. In other words, fruit juice (and even certain veggie juices) may push you over your keto-carb limit.
Fruits vs. Vegetables In Your Juice
When it comes to juicing, the possibilities are many. For instance, you could try any of following juice recipes:
- Kale, spinach, celery, and ginger “green juice”
- Apple, pear, and banana fruit juice
- Tomato, carrot, and strawberry juice
The first option is vegetable juice, the second is fruit juice, and the third is a combination.
Vegetable juice will be the lowest-carb, lowest-calorie option of the three — and likely best for weight loss. It’s also the type of juice most compatible with a keto diet.
Fruit juice, on the other hand, is high in a form of sugar called fructose. Excess fructose consumption has been linked to metabolic issues, liver problems, and other health concerns[*].
One observational study following 13,440 adults over six years found that each additional daily serving of a 12-ounce fruit juice consumed was linked to a 24% higher risk of death[*].
The key to healthy juicing (and healthy eating in general) is to use lots of vegetables. It might not taste as sweet, but you’ll be avoiding loads of unnecessary sugar.
Knowing all the pros and cons, if you’re still considering a juice-only fast, it helps to have a plan. This step-by-step guide will help.
#1: Set Your Schedule
How long will your fast be? Over which days will you fast? When will you make the juice? When will you be drinking juice?
For instance, you might plan out a three-day fast from Friday through Sunday. You’ll make a big batch of fresh juice each morning, storing “lunch” and “dinner” in the fridge.
Maybe you have your first juice at 10 a.m., your second at 2 o’clock, and your third at 6 p.m.
Having a schedule makes everything easier. No need to make multiple decisions each day. Simply follow the plan.
#2: Go Shopping
Once you set your schedule, you’re ready to go shopping. Here’s what you’ll need:
- A high-quality juicer
- Fresh fruits (preferably local or organic)
- Fresh vegetables (preferably local or organic)
- Purified water or spring water
- Seasonings, such as lemon juice, cayenne, or fresh ginger
Avoid excess sugar consumption (which can prevent weight loss) and keep your shopping list to around 80% vegetables.
For instance, your shopping list of organic produce might include:
- Green apples
#3: Do the Juice Fast
Now that you’re prepared, it’s time to execute your fast like a pro. Stick to your schedule, and everything should be alright.
If hunger pangs become excruciating, feel free to drink extra water or pre-made juice. Also, light exercise is a great way to get your blood moving and boost feel-good chemicals in your body.
Be aware that headaches, nausea, and fatigue are commonly reported side effects from juice fasting. These may occur to varying degrees.
#4: Ease Out of the Fast
Your digestive system needs time to recover after an extended fast. Yes, you need to put calories back in. But not all at once, and certainly not on the first day following your fast.
Instead, eat smaller portions to ease out of your juice fast. Think salads, soups, and easily-digestible healthy fats. Be sure to choose whole foods, not processed foods or junk food.
Most importantly, note how you feel before, during, and after your juicing adventure. Did you get better, worse, or stay the same?
The Bottom Line on Juice Fasts
Juice fasting has become a popular method to lose weight and “detox.” However, it comes with a number of health concerns, and there is no evidence supporting the idea that it cleanses the body.
Before you try this type of liquid fast, it’s crucial to understand the risk factors. Rather than following a vegan juice fast, you might want to consider doing a bone broth fast instead. Also, here’s a word of advice: Don’t try to be a hero with your juice fast. If you feel horrible, listen to your body and cut it short.
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