Fact-checked by Dr. Anthony Gustin, DC, MS.
Written by Emily Ziedman
From juice cleanses to cabbage soup diets to the grapefruit diet — people have been looking to quick fixes for weight loss since the early 1900s.
The grapefruit diet, in particular, has sparked the interest of thousands of dieters over the years. What is the grapefruit diet?
Turns out, you can just eat some grapefruit before each meal to kickstart weight loss, feel full faster, reduce your risk of heart disease, and burn belly fat.
Or is this diet — along with hundreds of others — an empty promise to a quick fix?
The grapefruit diet, along with a host of other fad diets, seems to find their way into the mainstream every few years. With obesity affecting an estimated 78 million adults in the United States, it’s no wonder that a quick and effective weight loss strategy is on the mind of many Americans[*].
But weight loss can be tricky, as can fad diets. There are crazier ones out there — but can eating grapefruit every day really help you shed pounds?
Let’s take a look at the science behind this citrus fruit diet and see if a reduction in calorie intake plus grapefruit is the key to healthy weight loss.
Although no one can point to the person who originally came up with the grapefruit diet, people have been using it since the 1930s as a tool for weight loss.
There are a few different versions of the grapefruit diet, all with one thing in common: consuming copious amounts of grapefruit.
The most common grapefruit diet looks like this:
- Cut back on sugar, refined carbohydrates, and starches
- Eat more foods high in healthy protein and fat
- Eggs and bacon for breakfast
- Salad with protein for lunch
- Non-starchy vegetables and protein for dinner
- Before bed: glass of tomato juice or skim milk
- ½ grapefruit must be eaten with every meal, or 4 oz. of 100% grapefruit juice
You’re only supposed to follow the diet for a couple weeks, so proponents typically recommend avoiding exercise during this time since you’ll be cutting calories significantly.
So the idea is that you consume some grapefruit or grapefruit juice before each meal, and voila — you’ll lose weight.
It sounds a bit like magical thinking, but to give it fair consideration, let’s take a look at the research that’s led so many people to try the grapefruit diet. First, flavonoids.
Flavonoids for Weight Loss
Grapefruit contains a group of phytochemicals called flavonoids. Flavonoids are known for their myriad health benefits, including anti-inflammatory, antioxidant, anti-carcinogenic, and heart health-boosting properties[*].
Naringin is a type of flavonoid that’s abundant in grapefruit and has found its way into the spotlight for its potential weight loss activity.
Much like other flavonoids, naringin displays both antioxidant and anti-inflammatory activity. What sets naringin apart is research that suggests that it may also be useful in treating obesity, diabetes, and metabolic syndrome[*].
In mice, naringin turns off pathways that lead to insulin resistance, and also increases fat oxidation (fat burning)[*].
When researchers turned to human trials, they continued to find some interesting benefits of grapefruit for weight loss. One trial split 91 obese subjects into several groups; fresh grapefruit, grapefruit juice, grapefruit capsule, and placebo.
The trial found that those consuming fresh grapefruit before each meal had statistically significant weight loss compared to the placebo.
Fiber and Water for Weight Loss
Impressive as this may sound, it’s important to keep in mind that fresh grapefruit would include fiber and water, which are naturally filling.
It may simply be the satiating effects of eating fruit before a meal that led to less caloric consumption. The researchers in this study stated that although the results were significant, the mechanism behind grapefruit’s weight loss potential is still unknown[*].
Nootkatone for Weight Loss
Nootkatone, an essential oil found in grapefruit, has also been studied for its potential to enhance metabolism and weight loss. Nootkatone is responsible for that distinct citrusy aroma that you smell whenever you slice into a ripe grapefruit.
The research on nootkatone as a potential weight loss aid is still somewhat preliminary.
One study found that when mice were given nootkatone long-term, they saw improvements in obesity and physical performance. The researchers propose that the effects are due, at least in part, to increased metabolism of fat and glucose in the muscle and liver[*].
Proponents of the grapefruit diet talk about the fruit’s ability to help you burn a significant amount of weight in a short amount of time.
Some people even claim you can shed 10 pounds in a week by following the guidelines.
There are four major problems with the grapefruit diet:
- You’re losing mostly water weight
- Crash dieting doesn’t work long term
- Severe calorie restriction messes with your hormones
- Grapefruit doesn’t support blood sugar
Let’s dive into these a little more deeply to understand why the grapefruit diet isn’t a sustainable strategy for weight loss.
#1: Losing Water Weight Isn’t The Same As Losing Fat
Crash dieting can often lead to rapid weight loss, but most of the weight you lose is actually coming from water, not fat.
When you restrict calories, your body uses up its stored fuel sources more rapidly. One of the first fuel sources to go is your glycogen (the storage form of carbohydrates) in your liver and muscle.
Each glycogen molecule is bound to water molecules. So, when you burn up this fuel source, you lose water along with it at a rate of three grams of water per one gram of glycogen[*].
When you hop on the scale after a few days of restricting food and notice a significant drop in the number, you can be sure that at least some of that loss is coming from water.
That’s why when you start to eat normally again, the number on the scale rises pretty rapidly.
But before you get too bummed out — it works the opposite way as well. After a couple of days of indulgence, you might gain anywhere from 1-5 pounds overnight.
A good portion of that weight is probably coming from your refueled glycogen stores that are holding onto water, not an increase in fat mass.
#2: Crash Dieting Doesn’t Work Long-Term
When you start to reduce your energy intake too quickly (like when following a crash diet), your body’s defenses kick in. When your body senses a season of famine, it will start to hold onto fat and slow down your metabolism.
Frustrating as it may be, your body developed this metabolic response over thousands of years to protect you from dying of starvation[*].
Studies have also found that severe crash dieting can affect your mood and mental health. You may experience a hint of this when you skip lunch and feel “hangry,” but it can actually get much worse.
Some people encounter severe psychological disturbance with a crash diet and rapid weight loss.
When you lose weight and restrict food to a point that’s unnatural — your body is going to fight back. This can show up as hormone imbalance, anxiety, depression, mood swings, and more[*].
#3: Severe Calorie Restriction Can Mess With Your Hormones
Your body evolved to store fat as fuel for future lean times, which means it doesn’t want to get rid of fat easily.
One of the primary ways your body fights back against weight loss is via your hormones. When you have a satisfying meal and your body is getting the nutrients it needs, it releases a hormone called leptin.
Leptin, also known as the satiety hormone, has an incredibly important job when it comes to weight management. It tracks how much food you’re taking in, how much you’re burning, and how much fuel you have in storage.
When your fat cells release leptin, they’re telling your brain that you don’t need any more food, and it signals you to stop eating[*].
With severe caloric restriction, your body doesn’t get the signal that you’re satisfied.
Leptin surveys the scene and doesn’t sense that you’re meeting your nutrient needs, so it hangs back and encourages you to keep eating. At the same time, out of fear that you’re going to starve, it signals your body to decrease your metabolic rate[*][*].
Even a year after crash dieting, the hormones that stimulate appetite can stay high.
So, if you want long-lasting weight loss, you need to eat enough so that your leptin signals correctly[*]. Severe calorie restriction is not a good approach.
#4: Grapefruit Doesn’t Support Blood Sugar Balance
When blood sugar is high, your body doesn’t burn fat for fuel because it’s too busy dealing with the sugar in your bloodstream.
As a side note, following a ketogenic diet takes the guesswork out of blood sugar balance because you’re naturally avoiding the foods that can cause it to spike.
Back to the subject at hand: one half of a grapefruit has 13 grams of carbohydrates and 8.5 grams of sugar[*]. If you start every meal with a half of a grapefruit, you’re adding sugar that takes priority over burning fat for fuel[*].
Blood sugar and insulin control are crucial for fat loss, so spiking your blood sugar before every meal is most likely not going to get you where you want to go long-term.
In addition to potentially messing with your hormones, metabolism, and blood sugar, the grapefruit diet poses a couple of other dangers to be aware of.
Following the grapefruit diet means you’re getting more of your fair share of grapefruit — and there can be some serious downsides to overdoing it with this particular citrus fruit.
Due to some of the active constituents in grapefruit, it can amplify the effects of certain pharmaceutical medications.
It does this by blocking an enzyme in your intestine that usually breaks down some of the drug before it enters your blood. This allows more of the drug into your system, which can cause all kinds of trouble, including liver damage and stronger side effects.
Grapefruit may interfere with the following medications:
- Anti-anxiety medications like Buspirone
- Statin medications like Lipitor and Zocor
- High blood pressure medications like Procardia
- Organ transplant rejection medications like Sandimmune
- Corticosteroids like Entocort and Uceris
- Arrhythmia medications like pacerone and Nexterone
- Antihistamines like Allegra
It’s always important to talk with your physician about any medication you are on when trying a new diet.
May Increase Risk Of Kidney Stones
Drinking 250mL/ day of grapefruit juice has been associated with an increased risk of kidney stones. Given that the diet recommends 4 ounces of grapefruit juice three times a day, this would be over the 250mL/day limit[*].
Although grapefruit has some great nutrients like vitamin C, minerals, and antioxidants, its macronutrient profile doesn’t work well for the ketogenic diet.
With 26 grams of carbs per fruit and virtually zero protein or fat, grapefruit is likely going to spike your insulin too much for you to stay in ketosis[*].
If you want to add more fruit to your diet, stick to lower carb fruits like blueberries and raspberries. You can check out our ketogenic guide to fruit here.
The Takeaway: Stick To Keto, Not to Grapefruits
Grapefruit may have some interesting compounds that support a healthy weight, but the research around the grapefruit diet is not very compelling.
It’s more likely that some of the weight loss people experience when following the grapefruit diet comes from losing water weight and is not sustainable.
The grapefruit diet is meant to focus on calorie restriction and recommends that you avoid too much physical activity, which isn’t very sustainable either.
For lasting weight loss, you should always include physical activity. And any weight loss diet that recommends you stay sedentary is a red flag.
Instead, consider trying a ketogenic diet. It’s a well-researched way to lose weight and improve your health long-term.