Animals and Their Bodies

October 7, 2012 7:53 PM

How do animals (in the wild) maintain their weight?

How do animals in the wild (not domesticated) maintain their weight? It seems most animals who live not domestically are able to maintain a perfect weight or body mass, not over or under (as long as they have enough food).

I guess I am wondering about this to see how it can apply to humans. Apparently we do not really need to count calories to maintain weight, but what is the mechanism that lets one do so?

posted by bearette to Science & Nature (18 answers total)

Animals in the wild are food limited, they do not have over abundant food hardly ever. When they do they tend to make more animals until the food runs out and they starve.

Seasonally over abundant food can certainly cause metabolic problems though; a classic example being laminitis in horses or cattle over exposed to too much grass in the spring. You might say, aren't ungulates naturally exposed to too much grass in the spring? but no, in the wild they do not have access to the kind of high nitrogen, weed free grazing they do in domesticity, particularly the breeds most prone to laminitis like island breeds which are chronically forage limited.
posted by fshgrl at 8:01 PM on October 7, 2012 [1 favorite]

Animals in the wild with access to easy calories will overeat until they're overweight.

Or put another way, when was the last time you walked 12 miles to get maybe a couple hundred calories worth of fruit? Maybe, cause you might have to fight for it or avoid being eaten by something else just as hungry.
posted by The Whelk at 8:04 PM on October 7, 2012 [3 favorites]

but what is the mechanism that lets one do so?

Keeping moving, not sitting and looking at a screen (Monitor/Television/Phone) for hours at a time.
posted by cashman at 8:05 PM on October 7, 2012

Best answer: Also most animals will eat and stock up in good times, then lose weight in bad times. The best examples is a brown bear who will gain 20-30% of their body weight (hundreds of pounds on Kodiak brown bear) during the months of summer in order to survive a long winter of hibernation. Pretty much any animal needs to go into the northern winter fat and sassy to make it out the other side and they are absolutely optimized to gain weight amazingly quickly when food is available. But it's not always available. a bear who has so much body fat it can barely waddle in October in Alaska is not "overweight", it's doing it right.
posted by fshgrl at 8:11 PM on October 7, 2012 [5 favorites]

Walk everywhere, hunt or forage for your food, and watch out for predators. Or swim/ run/ bike a few hours every day.

In high school, I swam a few hours every day after school to practice for water polo. I ate anything I wanted to and was fit. A few years later, I was in college and a slacker, and put on the Freshman 15.

I used to work with a semi-pro bike racer. She was tiny lady, but ate a TON. She had to, especially when she was gearing up for a big race.
posted by filthy light thief at 8:13 PM on October 7, 2012

Best answer: I've seen many a fat raccoon in my day. If they have access to garbage, they'll easily eat themselves into obesity.

Animals have to expend many more calories than we do to get the same amount of nutrition. A gorilla has to spend a significant portion of its day chewing their food. With the advent of cooking, early humans and modern humans are able to get more nutrition in much less time at a much lower calorie expenditure.
posted by xyzzy at 8:13 PM on October 7, 2012 [5 favorites]

Apparently we do not really need to count calories to maintain weight, but what is the mechanism that lets one do so?

That is not apparent. The mechanism is that wild animals spend the great majority of their energy expenditure in search of the next meal (or avoiding becoming another animal's next meal). How much energy do you expend walking from the computer to the kitchen?
posted by Tanizaki at 8:14 PM on October 7, 2012

Ways that people maintain their weight without counting calories:
Not continuing to eat when your stomach is full
choosing foods that aren't mostly corn syrup and preservatives
moving around during the day
not substituting eating/drinking for dealing with negative emotions
posted by bleep at 8:14 PM on October 7, 2012 [2 favorites]

Best answer: Feast and Famine: MRI Reveals Secrets of Animal Anatomy

Images revealed, for the first time non-invasively, how a snake adapts its internal organs in preparation for a big meal and during digestion, until it has disappeared completely.
...
"Pythons are renowned for their ability to fast for many months and ingest very large meals," explained Kasper Hansen, from the Aarhus University in Denmark. Modern scanning techniques have shown how extreme adaptations of the internal organs allow the snake to accommodate this 'feast and famine' lifestyle.

Fasting Burmese pythons (Python molurus) were scanned before and at 2, 16, 24, 40, 48, 72 and 132 hours after ingestion of one rat. The succession of images revealed a gradual disappearance of the body of the rat, accompanied by an overall expansion of the intestine, shrinking of the gallbladder, and a 25% increase in heart volume.

In short: animals also have extremely adaptable organs, allowing them to feast in a short period of time, and sustain their bodies through prolonged famine periods.

Humans have some ability to feast then survive famine, but this is because humans are good at storing fat during times of plenty, we are also excellent at surviving times of famine.
posted by filthy light thief at 8:19 PM on October 7, 2012 [1 favorite]

Squirrels bury nuts all summer long and eat them in the fall and winter and hopefully get adorably fat or they die. Nut and seed eating birds also stash food in trees. So many animals don't maintain their. They cycle up and down every year.
posted by srboisvert at 9:02 PM on October 7, 2012

Rats with ad libitum access to sugar solution will drink sugar solution in addition to eating chow, increase their total calorie intake, and start gaining weight. So it seems that a big factor in limiting weight gain in animals in the wild is just simple food scarcity.
posted by Nomyte at 9:34 PM on October 7, 2012 [1 favorite]

Best answer: If you're relying on what's available through hunting and foraging, and you eat when you're hungry and eat what tastes good when it's available, you will usually end up eating a fairly healthy diet. Sweet foods (except honey) are mostly fruits and sweet vegetables, which are also high in vitamins. Food that tastes umami — meat, fish and some veggies — is usually high in protein. Starchy food is, I think, fairly limited unless you cultivate it, and fairly bland, so not really preferred if tastier stuff is available, and people like to eat it with other stuff.

Gaining weight when a lot of high-calorie food is available is not a bad thing if you're dealing with an irregular food supply and the availability is seasonal. You body is storing calories for use when sufficient food isn't available.

I assume other animals have also evolved so that their taste preferences match their nutritional needs.

The problem is for us that we eat a lot of starchy food with just sugar added, or just glutamate added to make it taste meaty or cheesy when isn't really high in protein, and the famine we've been storing up fat for never comes.
posted by nangar at 10:07 PM on October 7, 2012 [1 favorite]

Animals (human or otherwise) with too much food will tend to get fat. Animals with not enough food will lose weight to an unhealthy degree and eventually starve to death.

What you're doing is kind of a "noble savage" fallacy applied to animals. Tons of animals starve to death when they can't find enough food. Animals who have access too much food, for example because they live near humans who feed them or leave garbage around, become overweight to an unhealthy degree.

Sometimes people have a similar belief that indigenous human peoples "live in perfect harmony with the land" or something. Except that throughout history native peoples have starved when they couldn't find food, just like anyone else. There is no magic solution or power that you're not aware of in certain animals or people.
posted by drjimmy11 at 10:21 PM on October 7, 2012 [7 favorites]

There's another factor, too: for prey animals, if they get too fat, they get slow, which means they're more likely to get picked off by predators.

There isn't any lesson here for you to keep your weight down.
posted by Chocolate Pickle at 10:22 PM on October 7, 2012 [1 favorite]

There is another factor which many of the responses above seem to be leaving out, and that is that while weight and calories have a direct correlation, metabolism is a complex system with feedback loops. There is a range of calories within which an organism can maintain a stable and healthy weight. It's not like a 10% increase or decrease on a given day or week is going to make a big difference overall. (Of course, over time it certainly would.)
posted by Nothing at 5:23 AM on October 8, 2012

different families of animals have different strategies regarding weight. mammals generally have a tendency to put on fat when food is available, as a reserve to survive the winter (or other hard times). the fat insulates them from the cold and provides energy, sometimes during a period of hibernation or inactivity or hardship.

birds in general are different - they are much more mobile. their strategy for surviving the winter or food shortages is to fly somewhere where food IS still available. most of the year wild, flighted birds have little fat on their body because being bulky makes them less agile fliers (bad for escaping predators or capturing food) and extra weight also increases their flight costs. srboisvert is right to note that rather than eating surplus food and storing it as fat, a lot of birds will stash extra food in caches and eat it when it is actually needed.

when birds are preparing for a long-distance flight, their hormone profiles change (triggered by day length or another environmental stimulus). their appetites increase and their bodies lay down increased fat stores which will be used as energy during the flight. But again, if they gain too much weight they are going to face unfavorable flight costs or in a worst case scenario, not be able to fly at all.

so in general, you will see wild mammals, your mammal pets, and your mammal friends put on extra weight when food resources are available. it is part of our mammal heritage. but not so much for birds, even pet birds (canaries, parakeets), even though they are usually kept in a cage with free access to as much seed as they'd like to eat, rather than having their food measured out each day as we do for pet cats and dogs.
posted by scrambles at 7:13 AM on October 8, 2012 [1 favorite]

There was an experiment done a few years ago (on humans) that kind of looks at what you're wondering about. Basically a group of volunteers all agreed to eat a totally controlled diet. Their breakfast, lunch and dinner and a daily snack were all prepared by the researcher with careful portion size measurements before and after each meal (e.g. exact count of every calorie and where they came from was accounted for). Also, careful estimates of everybodies caloric output was maintained. In this study the snack was the variable. Every day the subjects got yogurt sweetened with some mixture of aspartame and sugar so that some days it might have relatively few calories, other days a moderate amount, other days a huge number of calories - they didn't know which.

What the researcher found was that, despite not knowing how many calories were in the snack they were eating, a portion of her cohort was really good at adjusting how much dinner they ate to compensate for the extra calories they got during the day, with others ranging from so-so to abysmal at this task. I tried to find a website describing this study, but all I could find was 10,000 pages of woo, so, hopefully, your Google-Fu is stronger than mine.

The other thing to consider is, even if you use the imperfect guideline 3500 calories = 1 pound, your accounting only needs to be off by one lifesaver candy a day (≈50 calories depending on the flavor) over the course of five or six years to go from your ideal weight to morbidly obese.
posted by Kid Charlemagne at 8:40 AM on October 8, 2012

Also, animals obviously eat their food raw -- cooking makes more of the calories available, increasing the "efficiency" of our eating. yay.
posted by acm at 10:22 AM on October 8, 2012