A whole medium grapefruit contains about 80 calories. Half a medium grapefruit, the more common serving size, has roughly 40 to 60 calories depending on how large the fruit is. That makes grapefruit one of the lowest-calorie fruits you can eat, with a nutritional profile that punches well above its modest calorie count.
Calories by Serving Size
Most calorie counts you’ll see are based on half a grapefruit, since that’s how most people eat one. The FDA lists half a medium grapefruit (about 154 grams) at 60 calories and 11 grams of sugar. The Florida Department of Citrus puts it slightly lower at 40 calories and 8 grams of sugar per half fruit, likely reflecting a smaller reference size. In practice, the number depends on how big your grapefruit is.
Here’s what to expect based on portion:
- Half a small grapefruit (3-inch diameter): about 40 calories
- Half a medium grapefruit (3.5-inch diameter): about 50 to 60 calories
- One whole medium grapefruit: about 80 to 120 calories
If you’re tracking calories closely, weighing the edible flesh gives a more reliable number than estimating by diameter. Raw grapefruit runs roughly 40 calories per 100 grams of fruit.
Pink, Red, or White: Does Variety Matter?
Nutritionally, the differences between pink, red, and white grapefruit are small. Calorie and sugar counts are essentially identical across varieties, with both pink/red and white coming in at about 40 calories and 8 grams of sugar per half fruit. The main difference is cosmetic and flavor-related: pink and red varieties tend to taste sweeter, while white grapefruit leans more tart and acidic. Pink and red grapefruits do contain more of the plant pigment that gives them their color, which acts as an antioxidant, but the calorie impact is negligible.
What Else You Get for Those Calories
Grapefruit is remarkably nutrient-dense for a food under 100 calories. Half a medium grapefruit delivers 100% of your daily vitamin C needs and 2 grams of dietary fiber, which is 8% of the recommended daily value. That fiber content matters more than the number suggests, because much of it comes from pectin, a type of soluble fiber found in the white membranes between the segments. If you peel a grapefruit like an orange and eat it section by section rather than scooping it with a spoon, you’ll get more of those membranes and more fiber.
Grapefruit also provides a small amount of vitamin A (2% of the daily value per half fruit), along with potassium and water. The fruit is about 88% water by weight, which contributes to its low calorie density and can help you feel full on very few calories.
Whole Fruit vs. Grapefruit Juice
Eating a whole grapefruit and drinking grapefruit juice are not nutritionally equivalent, even if the calorie counts look similar on a label. Juice strips out the fiber, particularly the pectin-rich membranes that slow digestion and help regulate blood sugar. Without that fiber, the natural sugars in juice hit your bloodstream faster. You also lose the volume that makes whole grapefruit so filling. It’s easy to drink 16 ounces of juice in a few minutes, consuming the sugar of two or three grapefruits, while eating even one whole fruit takes time and effort.
Grapefruit, Insulin, and Weight
Grapefruit has a long reputation as a “diet food,” and there is some science behind the idea. A study published in PLOS ONE found that mice on a high-fat diet given grapefruit juice gained 18.4% less weight than controls. They also had 72% lower fasting insulin levels, 13 to 17% lower blood sugar, and significantly less fat buildup in the liver. Interestingly, the grapefruit juice didn’t reduce how much the mice ate. The benefits appeared to come from changes in how their bodies processed sugar and fat, not from appetite suppression.
Animal studies don’t always translate directly to humans, but the insulin findings are consistent with grapefruit’s low glycemic impact. For a fruit with natural sugars, grapefruit causes a relatively gentle rise in blood sugar, partly because of its fiber and water content.
Grapefruit and Medication Interactions
Grapefruit can interfere with how your body processes certain medications, and this is worth knowing even if you only eat it occasionally. The fruit contains compounds that block an enzyme in your small intestine responsible for breaking down many common drugs. When that enzyme is blocked, more of the medication enters your bloodstream than intended, essentially giving you a higher dose than prescribed.
In some cases, grapefruit has the opposite effect: it interferes with proteins that help your cells absorb a drug, making the medication less effective. The FDA lists several categories of drugs that can interact with grapefruit:
- Cholesterol-lowering statins
- Some blood pressure medications
- Anti-anxiety medications
- Certain heart rhythm drugs
- Some corticosteroids used for inflammatory bowel conditions
- Organ transplant rejection drugs
- Certain antihistamines
If you take any prescription medication regularly, check the label or ask your pharmacist whether grapefruit is a concern. The interaction applies to both whole fruit and juice.