Katmai National Park is proud of its full-figured bears, and wants Twitter to know.

The park in southwest Alaska shared a gif from its official Twitter of a June 29 picture of a brown bear looking svelte standing in a creek, followed by a picture taken Sept. 30 of a much heftier bear sitting in some brush.

“At peak season, brown bears can add up to four pounds of weight a day. Bear 409 looks like she had no trouble with that. (Yes, this is the same bear. We’re screaming.),” the tweet read.

The park service said bears can gain up to 4 pounds every day right before hibernation. (Katmai National Park)

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It appears those on social media are just as impressed by the bear's weight gain. The pictures, which were only taken three months apart from each other, have gone viral racking up over 150K likes and 27K retweets.

People were amazed – and pleased – at the quick transformation.

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Some suggested the bear might be pregnant, thus explaining the weight gain, but a National Park Service ranger said that was not the case.

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Alaskan brown bears typically begin to gain weight for the winter in July. Around this time, bears enter hyperphagia state and start eating non-stop to bulk up for the annual hibernation. Adult male brown bears can weigh more than 1,000 pounds by winter. Adult females average about 400 pounds before hibernation.