Can Eating Too Little Damage Your Metabolism or Make You Gain Weight?

In the fitness industry, it’s common to hear certain coaches and influencers say that eating too little hurts your metabolism and can cause you to gain weight.

In this post, we will clarify the intentions of these coaches and influences and debunk any myths surrounding this subject. Get ready for an insightful journey! 

To put it simply, if eating too little resulted in weight gain, then starvation wouldn’t exist. So, it’s important to clarify that consuming a very low-calorie diet, or eating too little, which results in a calorie deficit, does NOT cause weight gain. That was an easy explanation! 

Will a calorie deficit or low-calorie diet damage your metabolism? No, not exactly. 

In theory, if you eat less energy (calories) than you expend, you should lose weight. If you do the opposite (i.e. eat more energy than you expend), you should gain weight. One way to refer to this is Calories In, Calories Out, or CICO.

In order to understand CICO (calories in, calories out) and metabolic changes, it is crucial to grasp how our bodies utilize calories and how maintaining a prolonged calorie deficit can influence them. 

1. Resting Metabolic Rate (RMR):

RMR is the number of calories you burn each day just to breathe, think, and live. This represents roughly 60-75 percent of your calories burned each day. It depends on weight, body composition, sex, age, genetic predisposition, and possibly the bacterial population of your gut. A bigger body has a higher RMR.

2. Thermic Effect of Food (TEF):

TEF is the number of calories you burn by eating, digesting, and processing your food. This represents roughly 5-10 percent of your ‘energy out’.

In general, you’ll burn more calories in the process of digesting and absorbing protein (20-30 percent of its calories) and carbohydrates (5-10 percent) compared to fats (0-3 percent). 

You’ll also burn more calories digesting minimally processed whole foods compared to highly processed foods.

3. Physical Activity (PA):

This is the number of calories you burn from purposeful exercise like working out at the gym, walking, biking, running, playing, gardening, etc.

4. Non-Exercise Activity Thermogenesis (NEAT):

NEAT is the calories you burn through fidgeting, walking, working, staying upright, and all other physical activities except purposeful exercise. This varies from person to person and day to day.

Going back to eating too little…

Typically when you’re on a diet, the ‘energy (calories) in’ decreases, ‘energy out’ also decreases to align with it. 

• Thermic Effect of Food (TEF) goes down because you’re eating less.
• Resting Metabolic Rate (RMR) goes down because you weigh less.
• Calories burned through Physical Activity (PA) go down since you weigh less.
• Non-Exercise Activity Thermogenesis (NEAT) goes down as you have less energy.
• The number of unabsorbed calories decreases, and you absorb a greater portion of the food you consume. 

NEAT is likely what is affected the most during a long diet and is what makes people think they have a slow metabolism. For example, most people walk and spontaneously move less on a diet. Those on extreme diets, like bodybuilders, note that they even blink and talk slower as well as use their hands less during conversation.

So, if you are eating less but also moving less you may not be in as much of a calorie deficit as you thought you were which is why you aren’t losing as much weight as you want. Your metabolism isn’t damaged, it just slows down as a survival instinct due to less food intake. In another post we’ll talk about reverse diets, how to increase your metabolism, and eat more food without gaining weight after a diet phase.

Recommendations to maximize NEAT and minimize metabolism slowdown:

• Start at a slight calorie deficit then gradually decrease (if needed) over the diet period.
• Don’t diet longer than about 12 weeks continuously. I use periodization to break up diet/maintenance phases or diet/muscle gain phases to get the best results and help prevent weight regain. Long-term and aggressive diets do more harm than good.
• Track your steps and keep them the same (or increase them) during the diet period. Try for 8-12k steps per day as a goal.
• Lift weights to maintain muscle and strength. Some cardio workouts may be beneficial if you are sedentary and don’t/can’t get a lot of steps in.
• Work with me because I can take all the thinking and planning out of dieting so you can just do it!