Most Common Fitness Problems, According to a Dietician (And It's Not What You Think!)

A woman doing hip thrusts in a gym

Kerianne Los thought she was doing everything right. She worked out – hard – six days a week. Sometimes seven. She did a ton of cardio and ab exercises. She was incredibly careful with her food. But she kept gaining fat and getting father and farther away from her aesthetic goals.  

“I didn’t understand. I thought I should be shredded,” she says.  

Maybe she needed more cardio. More crunches. Fewer carbs. More restrictions. But no matter how hard she worked out and how little she ate, Los wasn’t seeing the results she wanted.  

Kerianne Los posing in a gym

Today, Los is a registered dietician and certified personal trainer. And she says she understands what she was doing wrong. It’s one of the most common mistakes that people make when they’re trying to improve their fitness, she says. And it’s probably not what you'd expect. 

"Most people would think the biggest issue is overeating and underexercising," Los says, "which would actually be a relatively easy problem to fix." 

The real culprit? Under-eating and overexercising, she says. 

"The overarching issue is people don't understand the equation it actually takes to get results and keep them. Often, they focus so hard on one piece of the equation and miss the other pieces," Los says. 

That full equation? Nutrition + training + hormone balance = results. 

And really, they're all related, she says. For Los, her nutrition was so out of whack that it disrupted her thyroid. And the added stress of overtraining just exasperated that, she says. 

Today, Los helps people balance that trifecta, as the director of personal training and nutrition at Pursuit Fitness in Colorado, and she also offers remote coaching. 


People eating healthy food

The nutrition piece of the puzzle is the biggest misunderstanding she sees with the gym crew. Many people don’t know how much they are eating in a day or how much they need to eat to create a physique change. And usually, people she sees aren’t eating enough, she says.  

“It’s counterintuitive because we’ve always been told if you want to lose fat, you need to eat less and go into a caloric deficit, and that’s true to an extent,” Los says. “But if we’ve been living in a caloric deficit forever, our body’s not going to want to give up body fat.”  

This downregulates your metabolism and the spiral gets worse, Los says. Not to mention other health issues.  

When people begin eating more and providing their bodies with nutrients, everything changes, she says. 

Getting a coach can be supportive, but even before that, it can be helpful to raise awareness; you can’t change something if you don’t know what needs to change, she says. That’s why she recommends most people begin tracking their food. It doesn’t have to be perfect, but she recommends comparing how much you’re eating to what online basal metabolic rate calculators suggests – just to get an idea what’s going on. If it’s low, that’s when she slowly begins adding 100 calories here or there, until her client is eating enough. 


The biggest issue Los sees with training is people doing too much cardio and too little strength-training. Often, she says, the mindset goes like this: “I’m going to lose all this body fat first, and then I’m going to build muscle.”  

“It just doesn’t work like that,” Los says.  

She recommends putting a greater emphasis on progressive strength-training and not worrying about the cardio (or slowly reducing it over time). More muscle boosts your metabolism, which makes it easier to lose fat, she says.  

A woman doing an overhead press

“And most people need to put on muscle to have the body they want – they just don’t realize it,” Los says. It’s been said a billion times before, she says, but lifting weights alone won’t turn you into the Hulk.  

Even more important than the aesthetic is how lifting weights builds your confidence and mental health, Los says.  

“When you improve the mental side, you start to identify as an athlete or as somebody who cares about your health, and the decision-making process becomes very easy: Does this align with the person I am and the goals I’m trying to accomplish? If the answer is no, the decision is made,” she says.  

As for adding strength-training into your workout, the biggest mistake many people make – a mistake Los made herself for years – is to lift weights with no plan. Ask a coach to write you a plan or tap into a free or cheap resource online.  

“Just have a plan when you go in,” Los says. “The biggest mistake I made early in my training career when I began lifting weights was I never followed a program or tracked my workouts, so I was spinning my wheels and wondered why I wasn’t progressing. Once I started following a real program, my results were like night and day.”  

Plus, she says, most people are busy. The last thing they want to think about is what to do at the gym. A program is already laid out for you. 


A mom and baby in the gym

Hormones are the most important piece of the equation. And Los understands this firsthand. Because her poor nutrition and high stress caused a thyroid disorder that made her gain 40 pounds in two months.  

“I was driving my body into the ground,” she says.  

Your body can only handle so much stress, and that includes psychological stress and physical stress, like a chronic caloric deficit and overexercising.  

You could also have excellent nutrition and a smart training program, but if you’re so stressed that it disrupts your hormones, you won’t see the best results. Often, people fight their body, thinking they just need to go harder, and that just makes it worse. 

“No. You need to take a chill pill and pull back a little bit,” Los says.  

A man massaging his trapsShe gave herself a year to repair her relationship with food and prioritize rest, high-quality sleep, recovery, and stress management. Today, Los doesn’t need to take thyroid medicine anymore. Of course, she’s not saying that will be everyone’s story and it's critical to work with a trusted medical professional on any hormone issues, but her point remains: Your hormones matter. And it might take some time and trial and error, but you can control your stress. That’s a big piece of your fitness puzzle.   

“Society always makes you feel like you’re not doing enough: more cardio, more dieting, more supplements. You constantly need to be doing more. Sure, this may work for a little while, but eventually your body is going to say, ‘No more,’” Los says. “Your body is meant to be fed, rested, and taken care of.”