Watermelon nutrition: glycemic index, calories, net carbs, diets
Introduction
Watermelon has become a symbol of summer in numerous cultures. It is refreshing, bright, and consists of more than ninety percent water, hence the name.
In this article, we will talk about the part of the watermelon that isn’t water, how it affects our health and how it fits in different diets.
Table of contents
Classification
In its botanical classification, watermelon is referred to as a pepo: a modified berry with a thick and hard outer rind. It is loosely considered to be a melon; however, it is not in the Cucumis genus of melons. Instead, it is in the same Cucurbitaceae family as melons, cucumbers, and pumpkins.
The stripes of a watermelon indicate its variety. There are over 1200 watermelon varieties; however, the most popular ones are the seeded, seedless, mini, or yellow and orange watermelons.
History
The origin of watermelon is disputable. Scientists agree that watermelon’s progenitor was cultivated in the continent of Africa. The debate starts with the question of where exactly.
5000-year-old remnants of watermelon seeds were found in Libya. In Egyptian tombs, there were not only 4000-year-old seeds but also paintings of watermelons. Centuries later, it spread and found popularity in Mediterranean countries (1).
Nutrition
Every part of the watermelon is technically edible; thus, it is considered to be a zero-waste food. Naturally, watermelon seeds and the rind have different nutrition values compared to the red flesh. The seeds are often roasted, and the rind can be used as a vegetable, stewed or fried, as well as pickled.
Some recommend incorporating watermelon seeds in traditional recipes, especially in areas where chronic hunger is an issue, as it is usually locally available and thrown away, to improve the intake of protein, fat, calcium, carbohydrate, phosphorus (2).
Macronutrients and Calories
Around 92% of a watermelon’s weight is water, and only the remaining 8% consists of nutrients.
One average serving size of watermelon per person is considered to be one slice or 280g.
A 100g of watermelon contains only 30 calories, while one average serving contains 84.
Macronutrients chart
Carbohydrates
The predominant macronutrients in watermelon are carbohydrates. Of the 8% nutrients of watermelon, 7.55g consists of carbohydrates.
The watermelon pulp is very low in fiber, containing only 0.95g of it. The other 7.15g are composed of net carbs.
One average serving size of watermelon provides 20g of net carbs.
The net carb content contains mainly sugars, such as fructose, glucose, sucrose, and only a small amount of maltose.
Carbohydrate type breakdown
Protein and Fats
The protein concentration is very low, with only 0.6g of it in 100g of watermelon. It also has an insignificant amount of fats; therefore, it is low in saturated fats and has no trans fats or cholesterol.
In protein quality breakdown, out of all the essential amino acids, tryptophan, threonine, and lysine are contained in equal amounts and have the highest concentration. The rest of the essential amino acids are also equal in amounts, but each makes up only 1% of the protein.
Seeds and Rind
Watermelon seeds have a lot more protein (around 8%) and fats (around 17%), as well as fiber (around 40%) and calories; however, it is much more difficult to consume 100g of watermelon seeds (3).
Another study about the nutritional values of watermelon seeds has found very different numbers, putting protein at around 34%, 32% fat, 27% carbohydrates, and 0.1% of dietary fiber (4).
The watermelon rind is rich in a non-essential amino acid called citrulline, which is also found in the flesh. Red flesh watermelon has slightly less citrulline than yellow and orange flesh watermelons (5).
Vitamins
Watermelon is an excellent source of vitamin A and vitamin C. It falls in the top 26% of foods as a source for these vitamins.
It also contains low to moderate amounts of B complex vitamins, particularly B1, B2, B3, B5, and B6. It is low in vitamin K and vitamin E.
Watermelons are completely absent in vitamin D, vitamin B12, and vitamin B9.
Watermelon seeds are rich in vitamin E and vitamin C (4). They are also much higher in vitamin B3 compared to the flesh (6).
The rind of a watermelon is richer in vitamin A and contains high amounts of vitamin C (6).
Vitamin coverage chart
Minerals
Watermelon alone is not a great source of minerals. However, watermelon pulp is relatively high in potassium, manganese, magnesium, calcium, and phosphorus.
It has moderate amounts of copper, iron, zinc, selenium, and choline. It is very low in sodium.
Watermelon seeds also contain appreciable minerals; calcium, phosphorus, magnesium, sodium, potassium, and zinc (3).
Mineral coverage chart
Glycemic Index (GI)
Based on the numbers from The International Tables of Glycemic Index, the glycemic index of a raw watermelon from Australia containing 10g of carbohydrates is 80±3. In parallel with that, a raw watermelon containing 25g of carbohydrates has a GI of 72±13. The difference in carbohydrate concentration is based on the season and the growing environment.
Based on these numbers, the average GI of watermelon is 76 (7).
Despite the high GI, watermelon’s glycemic load of 4-6 is low, meaning one serving of watermelon contains only 6g of carbohydrates.
According to Harvard Health Publishing, a raw watermelon has a GI of 76±4 (8).
Another study has shown different numbers for a GI of a watermelon. They found red-fleshed seedless watermelon to have a GI of 51±2. Red-fleshed seeded watermelon has a slightly lower GI of 48±1, with yellow-fleshed watermelon having an even lower GI of 47±2. This study has shown no difference between the GI of a red-fleshed seedless watermelon and the juice extracted from it. (9)
Other researches have shown that watermelon from the Philippines has a GI of 48±4 and Malaysian watermelon has a GI of 55±3 (10, 11).
A watermelon’s glycemic index can be high or low, depending on the maturity stage, fiber and fat content, processing and treatment of the sample, and other factors.
Despite all these positive effects, people with diabetes are advised to moderate watermelon intake and combine high sugar fruits with healthy fats, fiber, and proteins to slow the absorption of glucose into the bloodstream.
Health Impact
Diabetes
Watermelons have an average glycemic index of 76, but that number can change depending on the maturity and carbohydrate composition of the watermelon.
Watermelons get their bright color from a carotenoid called lycopene. This compound has gained attention from scientists due to its bioavailability and high absorption levels in a watermelon. It has been proven to positively affect the cardiovascular system while also playing a role in defending the organism from diseases such as diabetes and cancer (12).
Another important component of a watermelon is the non-essential amino acid called L-citrulline, which has been studied as a potential non-pharmaceutical treatment for insulin resistance (13). L-citrulline is contained in especially high concentrations in the rind of a watermelon.
Once again, the consumption of watermelon is advised alongside healthy fats, fiber, and protein, such as nuts, for people with diabetic conditions, in order to slow the absorption of glucose.
Cardiovascular
The amino acid L-citrulline can protect the organism not only from diabetes but can also have a positive therapeutic effect on people with high blood pressure or other cardiovascular diseases (13).
A study has shown that it can effectively reduce the extent of cardiovascular disorders (12).
Allergy
Watermelon allergies are quite rare but can still occur in both children and adults.
Three major allergens have been described in watermelons; malate dehydrogenase, triosephosphate isomerase, and profilin. Among watermelon allergic patients, the frequencies of sensitization to these compounds are 96, 78, and 56 percent accordingly (14).
These allergens usually cause oral allergy syndrome as the primary manifestation. It commonly presents with immediate swelling and an itching sensation in the mouth after consuming the food allergen (15).
The protein profilin can also be found in other fruits, such as melons and oranges․
Cancer
As stated previously, the carotenoid lycopene can also potentially have anti-carcinogenic qualities (12).
A group of compounds that the watermelon rind is also rich in is polysaccharides, such as arabinogalactan, galactose, arabinose, rhamnose, and others. These polysaccharides are known for their antiproliferative and antioxidant properties. The antitumor activity of watermelon rind has a significant cytotoxic ability against laryngeal carcinomatous cells (16).
Watermelon rind is also rich in anthocyanin and flavonoids, known for their antioxidant, anti-inflammatory, and anticancer qualities (17).
Pregnancy
The antioxidant lycopene has also been proven to have the potential to reduce the development of pre-eclampsia and intrauterine growth retardation in first-time pregnant women (18).
Watermelon can be advised to patients with hyperemesis gravidarum, a pregnancy complication characterized by severe nausea and vomiting, as the high water content can help stay hydrated (19).
Urinary System
Watermelon pulp is known to have protective properties in chronic kidney failure and the potential ability to clear urine. It has been proven to possess significant anti-urolithic and diuretic activities that can help people with bladder or urinary tract issues (20).
Watermelon Diet
As the name suggests, a watermelon diet is a diet during which you only eat watermelon. The high water content in watermelon makes this more of a cleanse than a diet.
Daily consumption of watermelon can lead to a reduction of body weight, body mass index, blood pressure, as well as improve some factors associated with obesity and being overweight. The mechanism for this action is watermelon’s ability to increase perceived satiety and moderate postprandial glucose and insulin response (21).
As a fruit, watermelon has a high density of water with low caloric intake, making it a perfect snack for people trying to lose weight. We’ve already talked about the health benefits of watermelon consumption; however, the watermelon diet is a radical form of dieting. Due to lack of protein and fats, it cannot be recommended to children, pregnant women, and people with conditions such as diabetes or malnourishment.
Watermelon in Diets
| Keto | The keto diet allows an average of 10-20% of your daily caloric intake to be carbohydrates (22). A 100g of watermelon contains only 8g of carbohydrates; therefore, watermelons can be consumed during a keto diet, with careful management of the carbohydrate intake. |
| DASH | Watermelons are suitable for the DASH diet due to their low sodium and high potassium, magnesium, and fiber concentrations. You can have 4-5 servings of fruits each day (23). |
| Atkins | You can have watermelon if you’re on the third or fourth phases of the Atkins 20 diet or the Atkins 40 diet. However, a cup of watermelon contains 11g of carbohydrates, so you have to eat it in moderation (24). |
| Mediterranean | The Mediterranean diet emphasizes using fruits and vegetables in your eating plan. Watermelon suits this diet perfectly. The Mediterranean watermelon salad is a well-known recipe. |
| Paleo | Even though prehistoric people probably did not eat watermelons, a moderate amount can be acceptable during a paleo diet. It is one of the few sweet fruits that can be used on a paleo diet (25). |
| Vegan/ Vegetarian/ Pescetarian | Since watermelons are plant species, you can naturally eat them on these diets. |
| Dukan | You cannot eat watermelons or fruits in general during the Attack and Cruise phases. You can add watermelon into your diet during the Consolidation phase, but only one serving a day. You can have moderate amounts of watermelon throughout the Stabilization phase (26). Watermelon overall is considered to be a Dukan-friendly food, depending on the phase you’re in (27). |
| Intermittent Fasting | Traditionally you should abstain from watermelon during the fasting period and eat it during the eating periods. However, some believe you can occasionally break the fast with a low-calorie seasonal fruit, like watermelon. |
| Low Fat & Low Calorie | Watermelon has almost no fat and since over 90 percent of it is water, it is one of the best fruits to eat during a low-fat or a low-calorie diet. A 100g serving of watermelon has only 30 calories. |
| Low Carb | Watermelon can be a great option to satisfy your sweet cravings during a low-carb diet, but only in moderation. Keep in mind an average serving of watermelon contains 20g of net carbs. |
| Anti Inflammatory | Watermelon is great for an anti-inflammatory diet due to its properties gained from lycopene, anthocyanin, and flavonoids (12, 17). |
| BRAT | If you are following the BRAT diet for a limited amount of time, you can add watermelon as bland food since it is an excellent source of hydration. However, you have to moderate your intake as large amounts of lycopene consumption can cause diarrhea (28). |
References
- The 5,000-Year Secret History of the Watermelon
- https://pdfs.semanticscholar.org/461c/4889b0ab6f8a34856e50aeac0a3f74d77af7.pdf
- https://www.researchgate.net/publication/323663320
- http://www.phytojournal.com/archives/2015/vol3issue6/PartB/3-6-24.1.pdf
- https://www.researchgate.net/publication/7736564
- https://www.researchgate.net/publication/259176510
- https://care.diabetesjournals.org/content/diacare/suppl/2008/09/18/dc08-1239.DC1/TableA1_1.pdf
- Glycemic index for 60+ foods
- http://www.ifrj.upm.edu.my/25%20(06)%202018/(41).pdf
- https://www.academia.edu/17584643/
- https://www.researchgate.net/publication/5488788
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4464475/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6073798/
- https://pubmed.ncbi.nlm.nih.gov/19295232/
- https://www.researchgate.net/publication/289039646
- https://www.researchgate.net/publication/333828166
- https://www.scientific.net/MSF.998.261
- https://pubmed.ncbi.nlm.nih.gov/12767566/
- https://pubmed.ncbi.nlm.nih.gov/33986063/
- https://pubmed.ncbi.nlm.nih.gov/29145146/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6470521/
- https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/ketogenic-diet/
- https://hypertensioninstitute.com/service/dash-1-2-diet/
- https://www.atkins.com/how-it-works/library/articles/national-watermelon-day
- https://paleogrubs.com/healthiest-paleo-diet-foods
- https://www.dukandiet.com/low-carb-diet/4-phases
- https://www.dukandiet.com/newsletter/june-2013
- https://www.cancer.gov/about-cancer/treatment/cam/patient/prostate-supplements-pdq
Important nutritional characteristics for Watermelon
Watermelon Glycemic index (GI)
Mineral chart - relative view
Vitamin chart - relative view
Protein quality breakdown
Fat type information
Fiber content ratio for Watermelon
All nutrients for Watermelon per 100g
| Nutrient | DV% | In TOP % of foods | Value | Comparison |
| Net carbs | N/A | 52% | 7.15g |
7.6 times less than Chocolate
|
| Protein | 1% | 89% | 0.61g |
4.6 times less than Broccoli
|
| Fats | 0% | 90% | 0.15g |
222.1 times less than Cheese
|
| Carbs | 3% | 54% | 7.55g |
3.7 times less than Rice
|
| Calories | 2% | 94% | 30kcal |
1.6 times less than Orange
|
| Starch | 0% | 100% | 0g |
N/A
|
| Fructose | 4% | 82% | 3.36g |
1.8 times less than Apple
|
| Sugar | N/A | 46% | 6.2g |
1.4 times less than Coca-Cola
|
| Fiber | 2% | 57% | 0.4g |
6 times less than Orange
|
| Calcium | 1% | 85% | 7mg |
17.9 times less than Milk
|
| Iron | 3% | 87% | 0.24mg |
10.8 times less than Beef
|
| Magnesium | 2% | 84% | 10mg |
14 times less than Almond
|
| Phosphorus | 2% | 92% | 11mg |
16.5 times less than Chicken meat
|
| Potassium | 3% | 80% | 112mg |
1.3 times less than Cucumber
|
| Sodium | 0% | 98% | 1mg |
490 times less than White Bread
|
| Zinc | 1% | 91% | 0.1mg |
63.1 times less than Beef
|
| Copper | 5% | 84% | 0.04mg |
3.4 times less than Shiitake
|
| Vitamin E | 0% | 91% | 0.05mg |
29.2 times less than Kiwifruit
|
| Vitamin D | 0% | 100% | 0µg |
N/A
|
| Vitamin C | 9% | 26% | 8.1mg |
6.5 times less than Lemon
|
| Vitamin B1 | 3% | 80% | 0.03mg |
8.1 times less than Pea
|
| Vitamin B2 | 2% | 90% | 0.02mg |
6.2 times less than Avocado
|
| Vitamin B3 | 1% | 88% | 0.18mg |
53.8 times less than Turkey meat
|
| Vitamin B5 | 4% | 79% | 0.22mg |
5.1 times less than Sunflower seed
|
| Vitamin B6 | 3% | 80% | 0.05mg |
2.6 times less than Oat
|
| Folate | 1% | 87% | 3µg |
20.3 times less than Brussels sprout
|
| Vitamin B12 | 0% | 100% | 0µg |
N/A
|
| Vitamin K | 0% | 88% | 0.1µg |
1016 times less than Broccoli
|
| Tryptophan | 0% | 97% | 0.01mg |
43.6 times less than Chicken meat
|
| Threonine | 0% | 96% | 0.03mg |
26.7 times less than Beef
|
| Isoleucine | 0% | 97% | 0.02mg |
48.1 times less than Salmon
|
| Leucine | 0% | 98% | 0.02mg |
135.1 times less than Tuna
|
| Lysine | 0% | 94% | 0.06mg |
7.3 times less than Tofu
|
| Methionine | 0% | 97% | 0.01mg |
16 times less than Quinoa
|
| Phenylalanine | 0% | 97% | 0.02mg |
44.5 times less than Egg
|
| Valine | 0% | 98% | 0.02mg |
126.8 times less than Soybean
|
| Histidine | 0% | 98% | 0.01mg |
124.8 times less than Turkey meat
|
| Cholesterol | 0% | 100% | 0mg |
N/A
|
| Trans Fat | N/A | 100% | 0g |
N/A
|
| Saturated Fat | 0% | 92% | 0.02g |
368.4 times less than Beef
|
| Monounsaturated Fat | N/A | 86% | 0.04g |
264.8 times less than Avocado
|
| Polyunsaturated fat | N/A | 90% | 0.05g |
943.5 times less than Walnut
|
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NUTRITION FACTS LABEL
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Health checks
Watermelon nutrition infographic
References
The source of all the nutrient values on the page (excluding the main article and glycemic index text the sources for which are presented separately if present) is the USDA's FoodCentral. The exact link to the food presented on this page can be found below.