It depends ...
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Cantaloupe (one 177g serving) contain 15g of Carbohydrate (with some being from fiber) and so it is not considered a Keto food, unless you count it as part of the 25-40g limit of carbs you'll have per day.
But here's the kicker; some of that carbohydrate (1.0g) is fiber which means that a whole serving has less than 14 grams of carbs in it.
As long as your total carb count at the end of the day is under 25-40g then eating any carb is fine, and cantaloupe is a healthy choice if you do eat it.
Cantaloupe has almost no fat and a small amount of protien which means it is not the typical, fat-heavy, low carb Keto food but it is still able to fit into the Keto diet if you choose to do so by eating smaller amounts.
Controlling insulin is key when it comes to the Keto diet and adding in smal amounts of cantaloupe is not a danger to your staying in ketosis unless you eat too much.
Eat and be healthy.
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