How Under-Eating Can Lead to Unintended Weight Gain

The average adult human body burns approximately 1,500 calories daily through its basal metabolic rate (BMR), a metric commonly referred to as “resting calorie expenditure”. This means that if one were to remain inactive for an entire day, the body would still burn around 1,500 calories to maintain essential physiological functions.

Resting calorie expenditure varies significantly based on factors such as age, height, weight, gender, and muscle mass. For instance, some individuals may have a resting expenditure of 1,200 calories, while others may reach up to 2,500 calories.

To determine daily caloric needs, it is essential to consider active calorie expenditure as well. This includes calories burned through any form of movement, from simple actions like nodding to structured exercise.

By combining the average resting calorie expenditure (1,500 calories) with an estimated active calorie expenditure (about 500 calories), we arrive at a total of approximately 2,000 calories. This average is why nutrition labels often base their recommendations on a daily intake of 2,000 calories.

So, how do we determine how much a specific person needs to eat if their goal is to lose or maintain body fat?

First, it’s important to define body fat. Body fat is stored long-term energy. There are two ways to gain body fat. The first, more commonly recognized, occurs when caloric intake exceeds caloric expenditure (we eat more than we burn). The leftover calories are then stored as body fat for future energy needs.

Body fat can also increase when caloric intake is insufficient over an extended period. In such cases, the body may enter a state of "fight or flight," causing it to store any consumed calories as fat to preserve energy reserves. During this state, the body tends to utilize muscle tissue for energy before tapping into fat stores, as fat serves as a crucial reserve.

Now, regarding the often-cited number of 1,250 calories: many diet programs and weight loss brands promote this as a "magic number." While it is true that consuming fewer than 1,250 calories may lead to weight loss, there is a limit. When caloric intake drops too low for too long, the body may respond with that “fight or flight mode” mentioned above.

Common indicators of inadequate caloric intake include low energy levels, difficulty gaining muscle mass, increased body fat, headaches, mental fog, and general fatigue.

A healthy caloric deficit for the average individual typically ranges from 400 to 700 calories per day. However, these numbers can vary significantly from person to person. Ultimately, effective weight management is not a one-size-fits-all endeavor; it is essential to tailor approaches to individual needs and circumstances.