5 Ways Undereating is Ruining Your Workout



Undereating Can Lead to Loss of Muscle Mass

In your quest to speed up weight loss, you chop your calories by 500 calories daily. While that might not seem unreasonable, it could still stymy your efforts to build and preserve muscle.  You’re not only cutting back on your calorie intake but burning more calories through exercise.  If you’re not eating enough calories, your body can, under certain circumstances, break down its muscle tissue for energy. Plus, to build more muscle, though, your body needs those calories and protein in the first place!

Eating enough food to maintain muscle is just as important as working out regularly. Without adequate calories and protein, you may lose weight, but it will be both body fat and muscle. Especially as you age, you need the extra protection against frailty that muscle mass offers. Plus, having more muscle gives your resting metabolic rate a subtle boost, so you burn more calories over 24 hours.

Don’t sacrifice muscle gains by undereating or skimping on calories. If you lower your calorie intake too low, your body will begin to protect your fat stores to conserve energy. Keeping a food journal can help you determine where you stand.

You Have Less Energy

You may have heard the saying, “You are what you eat.” This is true in more ways than one. Not only does your physical health depend on what you put into your body, but your mental health and well-being depend on it too. What you eat also gives you the energy reserves to get through your busy days at work or school and the supportive nutrients your body needs to function well.

When you consume too few calories, you may not have the motivation to gear up for a workout and you may find yourself being less productive in other aspects of life too. Plus, you’ll slow down and burn fewer calories, making it even harder to lose weight. Your body tries to compensate for less fuel by slowing down and moving less. It’s an example of an adaption for survival.

Exercise is Tougher and Performance Suffers

When you don’t eat enough, glycogen stores drop, and you don’t have the energy reserves to do intense strength training or high-intensity interval workouts that helps with weight loss. Exercise becomes tougher and you’re less likely to put forth your best effort.

You may be limited in the volume of exercise you can do to fatigue and not make the expected gains because you can’t advance your workout by using progressive overload. In a low energy state, your body can’t supply the fuel needed to keep going at the same pace or intensity as before.

The solution? Eat enough so that your body has all the nutrients it needs to get through daily activities and exercise. If you’re not eating enough calories from healthy sources like fruits and vegetables, lean protein and whole grains, the odds are high that any weight loss will be short-lived.

Recovery Takes Longer

If you want to grow muscle, recovery is part of the equation. Your muscles need time to rebuild and repair and they also need nutrients to do this, including protein and carbohydrates, along with a host of supportive players, like vitamins and minerals. If you’re in a low-energy state after a workout and you don’t replenish your energy stores, it can lead to a rise in cortisol, a stress hormone that breaks down muscle tissue. A sustained rise in cortisol, due to the stress of undereating, has other negative effects including:

  • A rise in blood sugar and reduced insulin sensitivity
  • Bone loss
  • Increased belly fat (due to fat redistribution)
  • Anxiety
  • Brain fog
  • Increased risk of infection due to changes in immune function

One reason it’s important to consume a post-workout snack of 3:1 carbohydrate to protein is to restore muscle glycogen and to give your muscles the protein they need to repair and rebuild.

Hormone Disruption

Hormones play a role in every aspect of health, including weight control and muscle gains. We already mentioned the effect undereating has on cortisol, a stress hormone, but it impacts other hormones that impact body composition too. For example, undereating can slow thyroid function and your resting metabolic rate, which can lead to weight gain. Chronically undereating can also lower testosterone and growth hormone, two hormones that help with muscle building and muscle preservation. When these hormones drop, it can also trigger bone loss.


Eating too little means you’re not getting the nutrients your body needs for health and to sustain exercise.  When you eat less, your body doesn’t get enough of the foods it needs to fuel workouts, recover from those workouts, build muscle mass, or boost metabolism. Plus, you can experience a drop in motivation and not feel like doing the things you should do to stay healthy.

If you’re undereating, it’s time to change. Your body needs good nutrition, and it’s not going to get enough of what it needs if you’re drastically cutting calories. Such an approach isn’t healthy or sustainable and any weight you lose using excessive calorie restriction will likely be temporary. Be smart and fuel up properly for your workouts!


  • Martin CK, Heilbronn LK, de Jonge L, DeLany JP, Volaufova J, Anton SD, Redman LM, Smith SR, Ravussin E. Effect of calorie restriction on resting metabolic rate and spontaneous physical activity. Obesity (Silver Spring). 2007 Dec;15(12):2964-73. doi: 10.1038/oby.2007.354. PMID: 18198305.
  • Fraser R, Ingram MC, Anderson NH, Morrison C, Davies E, Connell JM. Cortisol effects on body mass, blood pressure, and cholesterol in the general population. Hypertension. 1999 Jun;33(6):1364-8. doi: 10.1161/01.hyp.33.6.1364. PMID: 10373217.
  • “12 Symptoms of Undereating & Underfueling – Sports Nutrition.” 27 May. 2020, https://www.fwdfuel.com/symptoms-of-undereating/.

Related Articles:

5 Things That Happen When You Drastically Cut Calories

Is Crash Dieting Harmful to Your Heart?

Why It’s Time to Take a Break from Dieting

Metabolic Adaptations – 3 Ways Your Body Tries To Keep You From Losing Weight

What is Metabolic Compensation & How Does It Keep You From Losing Weight?

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