Many people believe: “Eat less + run more = definitely lose weight”. This formula sounds reasonable, but in reality it’s not that simple. Many people, despite running hard and eating very strictly, still have the same weight, or even increase.
Causes and solutions
Including the following specific causes:
1. Basal metabolic rate slows down
The human body has a very smart ability to adapt. When you reduce your calorie intake too suddenly, the biological system will automatically switch to an “energy-saving” state. Important hormones such as leptin, thyroid or testosterone change, causing the basal metabolic rate (BMR) to decrease. As a result, even when you rest, the amounts of calories your body consumes is less than before.
To overcome this, instead of cutting back drastically, adjust slowly, maintain a moderate deficit and combine strength training to maintain muscle mass, a factor that helps maintain a high BMR.
2. The thermic effect of food is reduced
Every time you eat, your body needs energy to chew, digest and absorb nutrients. That is the “thermic effect of food” (TEF). On average, TEF accounts for about 10% of total daily energy expenditure. However, when you eat too little, this effect is also reduced. For example, if you eat 2,000 calories, your TEF is about 200 calories, but when you only eat 1,200 calories, this number is less than 120 calories. This makes the body consume less energy.
Therefore, the diet needs to ensure adequate nutrients, especially protein and fiber, to maintain TEF and avoid falling into a state of “conserving energy” too much.
3. Spontaneous activity (NEAT) is reduced
It’s not just exercise that burns energy. Small daily movements like walking, climbing stairs, standing up and sitting down, or even fidgeting also contribute to burning calories, which is called NEAT (Non-Exercise Activity Thermogenesis).
When you eat less and exercise too much, your body becomes tired, leading you to unconsciously limit these activities. That causes the total amount of calories burned to decrease sharply without you even realizing it.
To improve, try to maintain an active lifestyle: walk more, choose stairs, and actively do light exercise even when you’re not exercising.
4. Energy consumed during exercise is also reduced
A surprising thing is that when the body lacks energy for a long time, it will become more “economical” even during exercise. This means you burn fewer calories for the same exercise. If a mile of running used to burn about 100 calories, after a period of overeating, the number may only be 90 calories. The fat loss effect is therefore reduced, even if you exercise more.
The solution is not to rely solely on running, but to combine it with other forms of exercise such as HIIT and strength training, and to replenish energy before and after exercise so that the body can function effectively.
5. When all factors add up
Each of these small changes, if standing alone, is not too significant, but when added together, they become a big barrier. BMR decreases, TEF decreases, NEAT decreases, and energy expenditure during exercise also decreases. All of these make the total amount of calories you burn much less than you think. You may think you are creating an energy deficit, but in fact your body has adjusted to maintain balance. And if you add stress, fatigue and overeating, it is not surprising that you gain weight instead of losing weight.
In short, eating less and running more does not always mean losing weight. Your body has a self-protective mechanism and when put in a state of excessive deprivation, it will respond by conserving energy. Therefore, instead of trying to “eat less,” you need a smarter and more sustainable strategy. A moderate calorie deficit, a balanced diet, combining running with strength training, and maintaining daily activity are the keys to real and lasting weight loss.
