High-protein diets are everywhere—but what actually happens to your body when you eat more protein than carbs? Here’s what dietitians want you to know.
First, a little about how carbs and protein work inside your body.
Carbohydrates are your body’s go-to energy source—especially for your brain and during workouts. That’s because they can be most easily converted into sugar or glucose. “Carbs are your body’s preferred source of quick energy,” Dawn Jackson Blatner, RDN, CSSD, told Health.
While protein can also be converted into glucose and used for energy, that process is slower and less efficient. “Protein can be used for energy, but it’s not ideal,” said Blatner. “It’s primarily meant for muscle building and tissue repair.”
Fat can be burned for fuel, too—producing ketones instead of glucose—and it typically occurs when you cut carbs drastically on a very low-carb or keto-style diet.
Because your body prefers carbs over protein or fat for energy, you might notice a slight shift in your energy levels once you start cutting carbs and adding more protein.
“When eating fewer carbs, you might feel fine during steady activities, but higher intensity exercise or fast thinking can feel tougher,” said Blatner. “Your body can adapt over time, but it’s not the right fit for everyone.”
Starting a protein-heavy diet can come with some noticeable short-term benefits—and a few potential drawbacks.
You May Feel Fuller, Longer
“When you compare calorie for calorie, protein makes you feel fuller than the other macronutrients (carbohydrates and fat),” Kerry Hackworth, RD, LDN, told Health. That can help reduce sugar cravings, and over time may support weight loss by helping you eat fewer calories, added Blatner.
You Might Have More Steady Energy—But Less Pep
Focusing on more protein may provide your body with “more steady energy and fewer ‘hangry’ crashes,” said Blatner. But if you eat too few carbs, you may also feel fatigue, brain fog, and irritability—especially during mentally or physically demanding tasks.
Your Digestion Could Slow Way Down
Fiber—which is only found in carb-rich foods like fruits, vegetables, legumes, and whole grains—keeps you regular. If your protein-rich diet doesn’t enough of these digestion-promoting carbs, you could feel some constipation and bloating.
Eating more protein over the long run can have some real benefits—but too much focus for too long can come with consequences.
Potential Benefits
Muscle maintenance and growth, and fat loss. This is especially true when you pair it with exercise, specifically resistance training.
Blood sugar regulation. Reducing your carb intake can help lessen blood sugar spikes.
Increased insulin sensitivity. Key for helping to manage or prevent type 2 diabetes or other metabolic issues.
Possible Downsides
Strain on the kidneys. Excess protein is filtered out through the kidneys. Over time—especially for people with existing kidney issues—this could lead to damage.
Loss of fiber. High-protein diets may exclude more fiber-rich foods and fall short on gut health and chronic disease prevention.
Who Should Consider Eating More Protein Than Carbs?
- Older adults (to prevent age-related muscle loss)
- People with type 2 diabetes or metabolic issues
- Individuals who want to lose weight
- Athletes focused on strength training or muscle gain
Who Should Be Cautious?
- People with kidney conditions
- Anyone with gastrointestinal issues who needs a high-fiber diet
- Endurance athletes who rely on carbs for energy
- Those prone to disordered eating
The goal of a higher protein diet isn’t to cut out carbs completely, but to prioritize quality in both protein and carbohydrate choices.
“Protein is powerful, but carbs aren’t the enemy,” Blatner said.
Tips to Follow:
Keep fiber-rich carbs in your diet. Think: whole grains, fruits, legumes, veggies, etc.
Focus on whole food proteins. Lean meats, eggs, fish, and dairy are better choices than ultra-processed options like protein chips and cookies.
Watch for changes in energy levels. If you start feeling fatigued, moody, or even constipated, it may be time to add some more fiber and carbs back into the mix.
Remember fats matter too. Avocados, nuts, seeds, and oils are needed for a well-rounded diet that can also reduce inflammation.
A high-protein, lower-carb diet can support weight loss, muscle maintenance, and blood sugar regulation—but it’s not a one-size-fits-all fix.
Your body’s metabolism, energy needs, and long-term health depend on balance. And while protein might be trending, fiber-rich carbs deserve a spot on your plate too.
