Is Watermelon Low FODMAP?
Fresh cut, perfectly ripe watermelon with a sprinkle of salt is one of the great joys of summer. Unless, of course, it isn’t. Watermelon is definitely a “best of times, worst of times” fruit for many people. Can it fit in the low FODMAP system? Not really.
Watermelon is not low FODMAP. A normal serving of one medium watermelon slice contains 5.1 grams of excess fructose, far exceeding the low FODMAP guideline of .15 grams. And the slice contains 2.3 grams of fructans, exceeding the stated fructan guideline of .20 grams.
In this post, we’ll look at the FODMAP content of watermelon. Like all fruits, watermelon contains fructose (lots of it, actually). Watermelon also contains fructans and polyols. The truth is, watermelon is just an all around bad choice for those eating low FODMAP.
FODMAP Content in Watermelon
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Watermelon has three types of FODMAPs: fructose, fructans and polyols. Having fructose doesn’t necessarily make a food high FODMAP. Instead, it’s the amount of fructose relative to the amount of glucose that matters.
If a food has more glucose than fructose, we say it has no excess fructose. If a food has more fructose than glucose, we say it has excess fructose. It’s the amount of excess fructose that determines whether a food is low FODMAP.
Unfortunately, watermelon has a lot of excess fructose. In fact, watermelon contains more than twice as much fructose as glucose. That’s why watermelon is often listed, along with high fructose fruits like apples and pears, among the worst foods for those following a low FODMAP eating plan.
The table below lists the glucose, fructose and excess fructose values for fresh watermelon at different serving sizes.
Glucose, Fructose and Excess Fructose in Watermelon
| Serving | Glucose (grams) | Fructose (grams) | Excess Fructose (grams) |
|---|---|---|---|
| 1 medium wedge | 4.5 | 9.6 | 5.1 |
| 1/2 cup, diced or balls | 1.2 | 2.5 | 1.3 |
| 10 balls | 1.9 | 4.1 | 2.2 |
Published low FODMAP guidelines state that a food should have less than .40 grams of excess fructose per serving. However, if other FODMAPs are present in the food, it should have less than .15 grams of excess fructose.2 As shown in the table above, watermelon far exceeds these values at normal serving sizes.
I emphasize “normal serving sizes” because I’ve seen references online and in low FODMAP books to ridiculously small servings. For example, a slice of pear that weighs 5 grams. That’s the weight of five small paperclips. A lot of non-digital kitchen scales can’t even weigh something that small.
The truth is, you can make any food low FODMAP if you make the portion small enough. But published FODMAP guidelines clearly refer to food at standard serving sizes. Suggesting that otherwise healthy adults eat tiny portions of food seems contrary to the research underlying the low FODMAP plan.
My belief is that adults should eat adult sized portions of foods they can tolerate. Having a healthy relationship with food is just as important to me as having a healthy body. If I can’t fit a food into my diet at some kind of reasonable serving size, I take it as a sign that I just shouldn’t eat it.
Okay, now that I’ve had my say, let’s look at the fructan content of watermelon. If watermelon causes digestive drama, you could be reacting to fructans rather than fructose.
Fructan Content of Watermelon
Fructans is the short name for fructooligosaccharides, one of the “Os” in FODMAP. Many studies have shown that watermelon is high FODMAP, with some specifically citing fructans as an issue.3
If you think fructans and fructose are related, you’re right. Fructans are basically a string of fructose molecules with a glucose molecule stuck on the end. Unsurprisingly, then, people sensitive to fructose may also have trouble with fructans. Though, unlike fructose, which is a sugar, fructans are a form of fiber.4
Concern about fructan content in food is relatively recent, so there’s not a long history of research on fructans. Fortunately, more food composition studies are starting to include data on fructooligosaccharides.
For instance, the US Department of Agriculture (USDA) recently published data on oligosaccharide content for products like almond milk and soy milk. I’m hoping the agency will add data for more foods in the future.
The next section describes how I estimated fructan content of watermelon based on publicly available research studies.
Methodology for Estimating Fructan Content of Watermelon
First, I looked for scientific studies on the fructan content of watermelon. I found some studies that list fructose and polyol content in watermelon, but only one study that specifically listed fructooligosaccharide content.
According to this study, watermelon contains an average of .81 grams of fructans per 100 grams of fruit.5 100 grams is the standard measure used in food composition tests and is about 3.5 US ounces.
Second, I used the average fructan value to create estimates of fructan content of fresh watermelon at different serving sizes. I determined the amount of fructan per ounce, then multiplied this by typical serving sizes, using data from the USDA’s FoodData Central Database.6
Estimated Fructan Content in Fresh Watermelon
| Serving | Weight (approx) | Fructans (grams) |
|---|---|---|
| 1 slice, medium | 10 ounces | 2.3 |
| 1/2 cup, diced or balls | 2.7 ounces | .60 |
| 10 balls | 4.3 ounces | .99 |
The recommended low FODMAP fructan intake for fruit is .20 grams per serving or less.2 As shown in the table, all normal serving sizes of fresh watermelon far exceed this amount. Just 10 watermelon balls have five times the recommended intake of fructans.
So, if you’re sensitive to fructose and fructans, watermelon is definitely on your no-go list. But even if fructose-based FODMAPs don’t cause trouble, you can still react to other FODMAPs in watermelon.
Are There Other FODMAPs in Watermelon?
As if very high levels of fructose and fructans weren’t enough, turns out watermelon also contains polyols (the “P” in FODMAP). The good news, if you want to look at it that way, is that some servings of watermelon do fit with FODMAP guidelines for polyol intake.
Polyols like xylitol, sorbitol and mannitol are found in many foods, particularly fruits and vegetables. They’re also used in processed foods, like ice cream, jams and chewing gum. Since these contain sugar alcohols and not actual sugar, the products are often advertised as “sugar free” or “no sugar added.”7
Many fruits, like peaches and apricots, have high amounts of the polyol sorbitol. This is also true for apples and pears. In contrast, watermelon has no detectable sorbitol, but does contain the polyol mannitol.5
Polyols are thought to cause intestinal issues in some people. However, since polyols are often found with other FODMAPs (like fructose), it’s difficult to isolate their specific effects.8,7 Moreover, polyols aren’t usually tested in food composition studies. As such, sometimes it’s hard to find data on the polyol content of foods.
Fortunately, watermelon is one of the fruits most studied by low FODMAP researchers. I was able to find several studies on the mannitol content of different foods, including watermelon. This allowed me to create estimated mannitol values for fresh watermelon.
Methodology for Estimating the Mannitol Content of Watermelon
First, as with fructan content, I looked for scientific reports that specifically discussed mannitol content in fresh watermelon.
The best report on the subject I found is actually the same one cited earlier. This report states that the mannitol content of fresh watermelon averages .12 grams per 100 grams of fruit. The report notes a standard deviation of .011. All that means is the watermelon tested for this study had a range of mannitol values between .109 grams and .131 grams.5
Second, also as above, I used the average mannitol value to create estimates of mannitol content of fresh watermelon at different serving sizes. I determined the amount of mannitol per ounce, then multiplied this by typical serving sizes provided by the USDA.
Estimated Mannitol Content in Fresh Watermelon
| Serving | Weight (approx) | Mannitol (grams) |
|---|---|---|
| 1 medium wedge | 10 ounces | .34 |
| 1/2 cup, diced or balls | 2.7 ounces | .09 |
| 10 balls | 4.3 ounces | .15 |
Low FODMAP guidelines suggest keeping mannitol content to less than .20 grams per serving. As shown in this table, some servings of watermelon actually meet this standard. A half cup of diced watermelon or 10 watermelon balls contain less than the recommended amount of mannitol. But, a medium wedge exceeds recommended mannitol intake.
So, if you’re not sensitive to the fructose or fructans in watermelon, it appears you could fit this into your summer barbeque. Just be sure to measure out a portion, rather than take a slice directly from the melon.
Final Thoughts on Watermelon and Low FODMAP Eating
Watermelon really is one of the worst fruits for low FODMAPers. Unless the only FODMAP you’re sensitive to is lactose, watermelon isn’t an option.
There are low FODMAP fruit alternatives, such as pineapple. Fresh pineapple is low FODMAP at normal serving sizes and canned pineapple contains no FODMAPs. I typically use pineapple as a substitute for watermelon during the summer.
Some people also have luck with honeydew. Honeydew does have excess fructose, but has safe levels of fructans and polyols. So, if fructose isn’t an issue for you, honeydew might be a good watermelon alternative.
Another option in cantaloupe. At present, cantaloupe tests within safe levels for all FODMAPs at normal serving sizes. Just be sure to watch portions, because cantaloupe will have excess fructose in larger portions.
The important thing is to focus on what you can eat. Sure, you may be facing a summer without watermelon. But you can still enjoy many fresh fruits and vegetables, gluten-free hot dogs and lactose-free ice cream. Eating low FODMAP doesn’t have to mean a bummer of a summer.
About the Author
Amanda Coleman, PhD, studies food culture and teaches a popular Food and Society course. Years of digestive problems led her to live low FODMAP. Now she uses her research and analysis skills to help others understand FODMAP essentials, so they can lead better, healthier lives.
