These past few weeks, after many years, I started counting calories again, with the goal of making weight for an upcoming master’s boxing match. I don’t need to lose much, and I’m not in a hurry, so I started with what seemed like a conservative goal of about 2,000 calories a day, hoping for a gradual weight loss.
Two days in, as I sat at my desk listening to the grumbles of my stomach, all I could think was: “How the fuck can anyone survive on a diet of 1,200 calories a day?” I’m in decent shape given that I’m a geriatric millennial parenting a hyperactive toddler in the midst of a pandemic, but I’m definitely not an athlete.
The collective wisdom, which I’ve heard all my life, is that if you are a woman looking to shed a few pounds, 1,200 calories a day is the proper amount, 1,500 if and only if you are active. The idea that a woman might lose a little bit of weight while eating 1,800 or 2,000 calories a day is almost unheard of, a feat you could only manage if you were an Olympic-level athlete who exercised for hours and hours each day.
1,200 calories is the number I’ve heard all my life, starting from the way-too-young age I first became aware of the concept of dieting, and is the number that makes up the foundation of pretty much every commercial diet plan out there, whether it’s the sturdy, old-fashioned WW (once called Weight Watchers) where you calculate points based on the nutritional value of a food item, or the new kid on the block, Noom, which has all the energy of an “I’m not like those other diets,” except that it is a diet, one that recommends eating 1,200 calories a day.
The suggestion of 1,200 calories a day is from the 1920s
The concept of 1,200 calories a day for weight loss has been around since the 1920s, due to a book called Diet and Health: With a Key to the Calories that was widely read by Americans. In spite of 100 years of evidence that this recommendation doesn’t work, the idea just won’t die. (Something else considered a “good idea” in the 1920s: Adding the radioactive element radium to toothpaste, food, and drinks, which only ended after a number of factory workers—mostly young women—died incredibly painful deaths from radium poisoning.)
These diets rarely work. A person might lose weight in the short-term, but eventually they get so hungry they’ll go off the diet, usually regaining whatever they lost, if not more. “A lot of my clients have tried 1,200 calories in the past,” said Jamie Nadeau, a registered dietician who focuses on helping people repair their relationship with food. “They either were not able to stick to it, because it is not enough food, or they did stick to it for a while, maybe even lost a significant amount of weight, but then either had a really poor relationship with food after that or gained all the weight back.”
There’s a reason for that, which has everything to do with the fact that, for the vast majority of women, 1,200 calories a day qualifies as a starvation diet. “For most women, you need more than 1,200 calories just for your normal survival functions in your body,” Nadeau said. “The fact that people are trying to live on that, exercise on that amount of calories, is just ridiculous.”
1,200 calories is half the average woman’s daily energy needs
According to recent research, published in the journal Science in August, the average adult woman between the ages of 20-60 burns about 2,400 calories a day. This is an average—woman who are smaller and/or have a slower metabolism will burn less, while women who are bigger and/or have a faster metabolism will burn more. As the lead author of the study, Herman Pontzer, a faculty member at Duke University, noted in an email to Lifehacker, 1,200 calories a day is roughly half of what the average woman needs.
Unlike what our fitness trackers will tell us, we also don’t start at some low base energy requirement, “earning” the right to eat extra calories every time we move. Instead, our bodies have evolved to use a relatively fixed amount of energy each day, a concept known as “constrained total daily energy expenditure.”
What that means is that although physical activity is extremely important for our long-term health, including weight maintenance, it doesn’t burn as many extra calories as we think, and it won’t lead to weight loss without a conscious effort to reduce the amount of food you are eating.
Instead, our bodies act as though our daily energy use is a fixed budget, one that it will shift around to various processes in order to have everything add up to the same number at the end of the day, only to start all over again the next day.
If we are sedentary, our body will divert that extra energy to energetically costly processes, such as our immune system and stress response, which in small amounts help us fend off infections and escape from danger, but lead to chronic diseases in large amounts.
If we are very active, such as when we are training for something, our bodies will burn more energy in the short term, but eventually, they will adapt, with our energy needs returning to an amount that is closer to our average daily amount.
If we happen to gain muscle during the process, our metabolism will go up, along with our average daily energy needs, due to an increase in the amount of fat-free mass in our body. Our hunger will also increase as well, as that is our brain’s way of keeping us at a stable weight, which in the course of human history, has been essential for survival.
1,200 calories a day is similar to the Minnesota Starvation Experiment
Given the average daily energy needs for a woman is 2,400 calories a day, this would make a 1,200 calorie a day diet on par with the Minnesota Starvation Experiment, which was conducted in 1944 to try and establish the best way to re-feed people suffering from starvation.
In this study, 36 young, healthy men were recruited for a year-long experiment. The first three months were spent calibrating the amount of food they needed each day. The next six months consisted of these volunteers surviving on approximately 1,570 calories a day, which was approximately half of their daily caloric needs. During these six months, they lost approximately 25% of their body weight. The final three months were spent letting participants eat as much as they wanted.
In addition to the weight loss, participants developed a preoccupation with food that lasted long after the starvation ended. They also developed issues like anxiety and depression, along with eating patterns similar to people with anorexia, bulimia, or binge-eating.
Participants in the Minnesota Starvation Experiment were highly motivated volunteers. They believed their participation in this experiment would improve the outcomes of starvation victims, while also living and eating in a highly controlled environment. Even then, they developed issues that lasted well after the period of starvation ended.
In real life, what usually happens is a person will go on a 1,200 calorie a day diet, survive on this amount of food for a few days, maybe even a few weeks if they are extremely motivated, at which point they will usually fall off the bandwagon, eating more to make up for the deprivation.
There’s also a good chance they might not be counting accurately. “[P]eople are terrible at accurately tracking what they eat,” Pontzer said. “It’s possible that dieters aiming for 1,200 calories a day would end up at a less extreme reduction.”
For the vast majority of people, these diets won’t work in the long-term, meaning they will eventually gain the weight back, while also developing a disordered relationship with food along the way. “What I hear the most about 1,200 calories a day is that even if they are able to stick to it, they are miserable,” Nadeau said.
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