Are You Eating Enough?

Are you eating enough? Even if you are trying to lose weight, chances are that you are still under eating. This is an incredibly common problem in today’s “eat less, move more” world of diet advice. Truth is, most people would see better results by increasing their caloric intake. Find out if you’re eating enough with my free worksheet.

There is a huge focus in the area of weight loss on eating less, but when it comes to food and working out, less is not always better. Yes, you need to be at a caloric deficit in order to lose weight. But, so many people underestimate how much energy their body needs just to be (also known as BMR or basal metabolic rate). 

If you’re exercising regularly, doing a good job of keeping your stress levels under control, and eating a diet that’s not full of junk but you still don’t feel great, you might be under eating. Feeling tired or sluggish and having your weight continue to creep up despite eating right and exercising regularly might be a sign of under eating.

But how do you know if you are eating enough? Honestly, most people who are struggling to lose weight or dealing with fatigue, are not eating enough. Eating too little on a daily basis slows down your metabolism and makes you feel less than optimal.  

Are you eating enough?

Our bodies are smart and as a survival mechanism, they evolved to keep weight on, especially during times when food is scarce. So when we chronically under eat, our bodies hold on to weight because they don’t want us to starve to death. It’s much easier than you think to accidentally not eat enough. We are constantly told that if we want to lose weight we need to eat less and exercise more. But what we don’t pay attention to is how much we need to eat to meet the very basic needs of our body. To fuel all of the cellular processes that need to happen in order to just keep you alive. If you aren’t eating enough to meet those energy needs, then you are going to feel tired, hold on to excess weight, and suffer from other undesirable health consequences.

what happens if you don’t eat enough

From a physiologic perspective, your body can’t tell the difference between healthy weight loss and a potential starvation situation. When we start to lose body fat (intentional or not), our bodies trigger complex hormonal signals that keep us from losing too much. This is why so many attempts to lose weight don’t work, it’s not that you lack willpower, it’s that you are trying to overcome the survival mechanisms that are hardwired into your body.

Calorie restriction ultimately causes your metabolism to slow. Part of this is due to the fact that a smaller body requires fewer calories, but there’s an additional metabolic effect that isn’t attributed to a smaller body size. [1] A study done on participants in “The Biggest Loser” showed that resting metabolic rate was suppressed by around 500 calories per day for six years after the competition ended. [2] Under eating also causes your body to release more of the hormones that drive hunger and decreases those hormones that are involved in making you feel satiated. [3]

signs your are under eating

You don’t have energy: Food/calories are fuel. They provide the energy your body needs for everything that happens in your body. If you aren’t eating enough, your body uses up the energy you are giving it and then demands more, leaving you feeling fatigued.

You have mood swings: Most of us have probably experienced that “hangry” feeling. Serotonin, a neurotransmitter, plays a role in both your mood and your appetite and is affected by hunger. People who have low serotonin have a more difficult time regulating their emotional responses. [4]

You feel cold: Calorie restriction (intentional or not) decreases your core body temperature. You need to eat a certain number of calories to meet the needs of your body performing essential tasks AND to keep you warm. One study suggested that people who follow a calorie restricted diet have lower body temperatures that those who do not. [5] Other studies show that this drop in body temperature is partly due to a decrease in the thyroid hormone T3. [6] Low thyroid is associated with low energy, low mood, and overall decreased health.

You aren’t sleeping well: Not eating enough can make it difficult to fall asleep and stay asleep. There are studies that link not eating enough with a decrease in deep sleep (this is the sleep where your body makes important repairs to tissues and organs) and decreased sleep quality. [7]

Your hair is falling out: Hair loss is a sign of both not eating enough calories and not enough protein. When you aren’t eating enough, your body prioritizes the health of critical organs (like your brain and your heart), not things like hair, skin, and nails. Calories and protein aren’t the only things that matter when it comes to reversing hair loss, there are a lot of other critical nutrients to consider as well. [8]

How Many Calories Do you need?

For the sake of simplicity, let's talk about how this applies to you if you are trying to maintain your weight. I'm going to use an example of a 27 year old female who is 5'7" tall and weighs 123 pounds (please note, this is not a real person). 

I'm not going to walk you through the BMR calculation, you can find an online calculator or look up the equation to do it yourself. It's pretty simple math, but it's not exactly important to our discussion here. So, this example person has a BMR of 1377 calories. That means that if she sat completely still all day long she would need 1377 calories to stay alive. 

Side note: please appreciate the fact that the person in this example is not short and she’s pretty slim and her BMR is over 1300 calories. We have this idea in our head that 1200 calories is an appropriate amount to eat if we want to lose weight, but in almost all cases, that’s not enough to meet the MOST BASIC needs your body has.

If she works out about 5 times per week and she wants to maintain her weight, we need to figure out her total daily energy expenditure or TDEE. To do that we take her BMR and multiply it by an activity factor of 1.5 (for her 5 times per week workouts) and we get 2065.5 calories

Want to know your numbers? 

Click the button below to download a free worksheet to help you calculate this information for yourself!

What does this number mean? It means that she needs to eat 2065.5 calories everyday to maintain her current weight. Based on these calculations, she is burning 688.5 calories per day (TDEE-BMR = 688.5). If she were to burn more than that for whatever reason, she would need to eat more to maintain her weight. 

Now, how does this apply to weight loss? Let's take the same calculations for simplicity (I DO NOT think this person actually needs to lose weight, 123 pounds is pretty low for someone who is 5'7"). So we know that her TDEE is 2065.5 and she wants to lose weight. I prefer a percentage caloric deficit vs. a solid number (many people use a 500 calorie per day deficit) because that scales it to your activity level rather than being just an arbitrary number. 

A good place to start with a percentage is 15-20%, and remember, more is not always better. So for this example let's use 15%. A 15% deficit off of the 2065.5 calorie TDEE is 309.8 calories. So she will eat 309.8 calories fewer per day to lose weight. That puts her intake at 1755 calories per day. 

We can use the same formula of TDEE - BMR = 688.5 calories burned in a day to know whether or not she is eating enough. Since we created the deficit off of her TDEE, we don't need to do any math here. If she burns more than 688.5 calories in a day, she needs to add those calories back in. 

I advise almost every single patient that I see to eat more, even if they want to lose weight. I have yet to come across a patient who has complained about continued weight gain despite increasing their caloric intake. Obviously, what you’re eating matters, you can’t eat 2000 calories of chocolate cake and expect to feel good. But if you are under eating and expecting to lose weight, I can almost guarantee you that it won’t work, especially not in the long term.


1. Rosenbaum, Hirsch, M.J., Gallagher, D.A., & Leibel, R.L. (2008). Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weightThe American Journal of Clinical Nutrition, 88(4), 906-912. doi: 10.1093/ajcn/88.4.906

2. Fothergill, E., Guo, J., Howard, L., Kerns, J., Knuth, N., . . . & Brychta, R. (2016). Persistent metabolic adaptation 6 years after “The Biggest Loser” competitionObesity24(8), 1612-1619. doi: 10.1002/oby.21538

3. Sumithran, P., Prendergast, L., Delbridge, E., Purcell, K., Shulkes, A., Kriketos, A., & Proietto, J. (2012). Long-term persistence of hormonal adaptations to weight lossObstetrical & Gynecological Survey67(2), 91-92. doi: 10.1097/ogx.0b013e318247c6f7

4. University of Cambridge Research. (2011). Serotonin levels affect the brain’s response to anger.

5. Ishii, S., Osaki, N., & Shimotoyodome, A. (2016). The effects of a hypocaloric diet on diet-induced thermogenesis and blood hormone response in healthy male adults: A pilot study. Journal of Nutritional Science and Vitaminology, 62(1), 40-46 doi: 10.3177/jnsv.62.40.

6. Soare, A., Cangemi, R., Omodei, D., Holloszy, J. O., & Fontana, L. (2011). Long-term calorie restriction, but not endurance exercise, lowers core body temperature in humansAging3(4), 374-379.

7. Karklin, A., Driver, H., & Buffenstein, R. (1994). Restricted energy intake affects nocturnal body temperature and sleep patternsThe American Journal Of Clinical Nutrition59(2), 346-349. doi: 10.1093/ajcn/59.2.346

8. Guo, E. L., & Katta, R. (2017). Diet and hair loss: effects of nutrient deficiency and supplement use. Dermatology practical & conceptual7(1), 1-10. doi:10.5826/dpc.0701a01