According to research by scientists in the US and Brazil, the blue whale is the fattest animal on Earth, with the highest percentage of fat among mammals - more than 35%. With a weight of up to 180 tons, the blubber of a blue whale quickly reaches 63 tons.

However, one possible way to measure fatness is by body mass index (BMI), the weight ratio to the square of height. However, BMI may not be a reliable indicator of fatness in animals with different body shapes and proportions than humans. Another possible way to measure fatness is by body fat percentage, the ratio of fatty tissue to total body mass. However, body fat percentage can vary depending on the animal's season, diet, and activity level.

Using either method, some of the fattest animals in the world are marine mammals, such as whales, seals, and walruses. These animals have a thick layer of fat that helps them retain heat and store energy in the frigid ocean waters. For example, the blue whale, the largest animal that has ever existed, can weigh up to 200 tons and have a BMI over 40. Elephant seals, the largest seal species, can weigh up to 5 tons and have proportions—body fat percentage above 50%. The walrus, the largest of the pinnacles (a group that includes seals and sea lions), can weigh up to 2 tons and have a body fat percentage of over 30%.

However, not all the fattest animals live in the water. Some terrestrial animals are also high in fat for insulation or energy storage. For example, hippos, the third largest land mammal after elephants and rhinos, can weigh up to 4 tons and have a BMI over 30. Camels and domesticated animals can survive in these conditions. Harsh deserts can weigh up to 1 ton and have a body fat percentage of over 20%. Polar bears, the largest carnivores on land, can weigh up to 700 kg and have a body fat percentage of over 40%.

Therefore, there is no definitive answer as to which animal is the fattest in the world, as different methods of measuring fatness can yield different results. However, some candidates for this title are marine mammals that have adapted to living in cold water by developing thick layers of fat. Other candidates are terrestrial mammals that have evolved to cope with extreme temperatures or food scarcity by accumulating stored fat.

We detail some of the fattest animals in the world below:

1. The hippopotamus is one of the fattest animals in the world, known for its massive appearance, but 18% of its 1.5-ton body is skin. Under the 5cm thick layer of skin is a relatively thin layer of fat.

1. Camels have humps to store nutrients and fat. These tumors can weigh up to 35 kg. Fat is not only for keeping warm. When metabolized, it provides essential water for desert animals. The fat in the hump reduces heat to the rest of the body, helping them withstand the hot environment.

1. Some insects are considered fat for their size. Moths and larvae are known as high-fat snacks by Aboriginal Australians. Cossid moth larvae (Endoxyla leucomochla), also known as witchetty larvae, contain 20% fat, while adult Bogong moths have up to 39%.

1. Another type of fattest animal in the world is the night moth. Insects in the western United States grasslands appear abundantly in the spring. Around June, they migrate to alpine climates, where they feed on wildflower nectar. The night moth is the fattest in the animal kingdom, with 72% of its body fat in autumn, helping them survive the cold winters.

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