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How Not Eating Enough Affects Training Seasons

I know I haven’t written about running as much lately – mainly because I’m not training for anything (except a baby), but I still talk about running and training daily with many of my clients.

Many of my clients are training for a spring race or marathon. Therefore, it’s important we talk about the importance of changing up nutrition in tandem. Undereating and running can be very dangerous and lead to many other complications.

Like I talk about with relative energy deficiency, it’s so important to step up nutrition when you step up training (distance and/or intensity).

And by that, I mean, start paying more attention to what you’re eating. You likely need to be eating more.

Whether you’re graduating from the couch to a 5k, a 5k to a 10k, or a half marathon to a full marathon, you need to change the way you eat (for training and recovery), or you won’t see results.

Why Undereating and Training Don’t Mix

I often see people prioritize their training plan, but don’t equally prioritize nutrition. People still think you can “get away with whatever you want to eat,” if you’re marathon training.

However, undereating and not properly carb loading, or having sufficient glycogen on board can quickly lead to hitting the wall in a marathon.

While I see where that idea comes from (sometimes it can be hard to get enough calories), that mentality often de-emphasizes the importance of quality foods for your training and recovery.

Athletes performance plate

Training means you have to eat more, and oftentimes, more often. You also need to eat quality foods, including adequate macronutrients and antioxidants. You can’t expect to achieve good results or avoid injury if you are underfueling.

We talk about this often in our performance plates posts!

With clients, we work on what this fueling plan looks like. Intuitive Eating can still play a part in endurance training (more on intuitive eating and exercise here).

Not Hungry After a Workout Leads to Underfueling

Oftentimes, you may not feel hungry after a run. In fact, this is very common. If you’re not hungry after a workout, there are still several things you can do!

There are going to be times where you have to use your head, not your body, to make your fuel and recovery choices if you want to perform well.


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Oftentimes, when I meet with clients and calculate their needs as they increase their running times and distances, they are surprised when I tell them how much they should be eating.

It’s easy for us to forget how good our bodies are at using fuel when we let them.

toast with eggs next to tomato soup

Effects of Not Eating Enough

Here are some signs that your nutrition may not be matching up with your training.

You Feel Fatigued and Slow to Recover

Exercise is a stress to the body. I’ll say that again. Exercise evokes stress on our bodies. In most circumstances, this is a good stressor that our bodies are equipped to handle.

But, if we’re already stressing our bodies (maybe from a night of poor sleep, battling a cold, or undereating), exercise can cause more damage. 

A focused desire to exercise in these instances can lead me to question whether compulsive exercise is at play. 

woman stretching over blue yoga bowl

When our bodies are constantly stressed from excessive exercise and insufficient recovery, they start to break down. You may notice your body won’t recover as quickly.

Or, your times and splits may become slower. You may even feel fatigued earlier into your workouts.

These are signs of overtraining/undereating, and a signal from your body to change things up.

Add in some more rest days, or focus on some changes in your nutrition plan.

Garmin watch

You Constantly Feel Cold and/or Your Hair is Falling Out

When your body is lacking energy (read: calories), you may see changes in your skin and hair. Dry skin and hair loss are common symptoms of undereating.

When our bodies aren’t receiving adequate energy, they are smart and will do their best to protect us.

That being said, they will selectively decide where to put the energy they do have, which will go towards pumping the heart and keeping the brain functioning.

Without enough energy to generate heat, our temperature regulation gets put on hold (1).

Therefore, you may feel cold all the time.

You’ve Lost your Period

Females, this one is directed towards you. While there may be medical reasons for this (always check with your medical practitioner), irregular periods, or lack of a period completely is a red flag.

It typically signals an inadequate amount of energy that your body can readily use.

Like mentioned earlier, your body selectively shuts down certain processes when you are low on energy. You don’t need to menstruate to survive, so the body lets that go.

What makes this a serious concern is the potential for developing the Female Athlete Triad.

The Female Athlete Triad is characterized by low energy availability, functional hypothalamic amenorrhea (lack of period), and osteoporosis.

This is most commonly seen in female endurance athletes. It is possible to reverse, and often looks like some combination of an increase in calories and a decrease in exercise.

What Does Adequate Fueling Look Like?

We’ll cover this in another post, but you can find more information here, here and here. The main issue I see in athletes is inadequate carbohydrate intake before runs, and inadequate balanced meals and snacks after long runs and workouts.

As the “low carb” diet for runners continues to gain interest and momentum to “burn more fat” while running, know that no studies show that this way of eating improves performance, if that’s what you are after.

You need carbohydrates and glycogen to prevent you from hitting the wall and have those last minute sprints available to finish.

Carbohydrates are the predominant fuel for exercising muscles in terms of intensity and performance (2). 

We need adequate fuel for our bodies to function normally and optimally, and that goes for all of us beyond just athletes.

But, if you are starting a training session or getting ready to begin one, don’t forget about the importance of fueling and nutrition.

If you have specific questions about matching your nutrition to your training, I can help!

Chocolate milk after a run

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