Why You Sometimes Feel Sick When You Eat Healthier

Why You Sometimes Feel Sick When You Eat Healthier

You’ve committed to a healthier lifestyle and are exercising several times a week. You’ve replaced the junk food snacks, processed foods, and refined sugars with weekly meal prep and healthier, portion-controlled snacks.

So how come your whole body hurts and your stomach is off?

Any time you change up your diet, you might feel a little different for a while.

Here’s what happens to your body when you eat healthier (and why you shouldn’t give up on your new habits).

Why Your Diet Might Be Making You Feel Sick

Feeling a bit ill after taking up a healthier lifestyle is extremely common. But, if you have any doubts, please contact your doctor to be on the safe side.

If you’ve recently made a robust or abrupt switch, you might not feel your best straight away. Here’s why.

1. You’re not staying hydrated

Some diets, especially low-carb diets, can cause your body to shed excess water.

Even if you maintain your usual amount of water consumption, you might find yourself mildly dehydrated, which can cause dizziness, rapid heartbeat, and faster breathing.

A good indicator of your level of hydration is the color of your pee. The lighter yellow, the better. Dark yellow pee is a clear sign that you need to drink water, stat.

2. Your diet is too extreme

Transitioning from a standard American diet to a calorie-restricted one or a strict elimination diet (think: keto or vegan) on a dime can also be a shock to the body.

“When you take out all the grains, you also lose fiber,” says Tucker. “Complications like constipation can become a real issue. No matter what diet you’re on, you need lots of fiber to keep your digestion moving.”

If you’re cutting out meat or other animal products, make sure you’re replacing them with healthy whole foods, like lean proteins and healthy fats.

3. Your diet is missing essential nutrients

Eliminating whole categories of foods like nightshades or legumes (unless there’s a medical reason to do so) may also eliminate essential nutrients from your diet.

“When you completely eliminate any food category, you also eliminate the nutrition that food would provide,” Tucker says. “If you eliminate a category of foods, take care to source key nutrients from other places.

At the same time, if you are eating a ton of bacon and avocado but never touching a veggie, your body may be telling you that your nutrition is lacking.”

4. Your diet is too low in calories

Your brain and body needs a steady supply of calories to function normally. If you’re not filling your plate with enough to get your body through the day, you won’t feel your best.

On most diets, “carbs fuel your brain,” says Tucker. “On low-carb diets, like the ketogenic diet, fats fuel your brain.”

Either way, she adds, you need to eat enough food.

“Too much calorie restriction causes your body to run out of short-term fuel in the form of either fats or carbs,” Tucker explains. “That alone can make you feel sick.”

What Happens to Your Body When You Eat Healthier?

When you shift to a healthier lifestyle and commit to cleaner eating and regular exercise, your body can experience a whole lot more than weight loss.

Your diet can impact your brain chemistry, your gut microbiome, and even your hormone production.

Here’s a look at what happens when your clean up your eating and how that affects different areas of your body.


Some of the most common digestive symptoms you may experience are:

  • digestive slowdowns (or occasional constipation, due to a low-fiber diet or not drinking enough fluids)
  • more trips to the bathroom (due to increased fiber intake)
  • stomach cramps (thanks again, fiber!)
  • nausea

Your gut microbiome can change within days of altering how you eat, so you may be feeling the effects of that shift, “especially if the old you was snacking on lots of processed food,” says Barbie Tucker, R.D., L.D., M.Ed, a registered dietitian who practices in the Atlanta area.

And, if you’ve shifted to, say, a ketogenic or other low-carb diet, your body might slow way down due to a lack of complex carbs and, thus, fiber.

“We are supposed to be getting 25 to 30 grams of fiber daily,” says Tucker.

“If you find that you are unable to use the restroom, that might be an indicator that you lack adequate fiber in your new diet.”

And on the flip side, your body may be used to digesting a whole lot of sugar and simple carbs, and now it’s being asked to work harder to break down more nutrient-dense fare that’s higher in fiber.

“Most often lack of fiber or inadequate hydration are to blame when digestive issues arise,” says Tucker. “Take stock of how regularly you drink water and consider whether or not you include enough fiber in every meal.”

Brain health

On a mission to cut out added sugars? You may experience:

  • headaches
  • nausea
  • dizziness

A study conducted with mice showed that when cutting back on added sugar, it takes time for the brain to acclimate to not getting the regular hits of dopamine sugar provides.

One human study suggests that there are adverse effects of prolonged sugar intake (from sweet food or beverages) on long-term psychological health. It also suggested that lower intake of sugar may be associated with better psychological health.

Sugar detox symptoms are common and usually subside in just over a week.

“If your brain is accustomed to a consistent supply of sugar — via flavored beverages and sugary treats, not to mention the hidden sugars in products like bread and processed foods — a sudden halt to the sugar supply can make you feel less than your best,” says Tucker.

Mood and energy levels

With food and mood, it’s important to know that most serotonin receptors are located in the gut.

The gut and the brain communicate via the vagus nerve, and this communication highway demonstrates the importance of food quality to your everyday mood.

2019 study suggests that eating a healthy Mediterranean-style diet may help protect against mood disorders.

“Your brain consumes a lot of energy,” explains Tucker. “It lives on carbs. Our bodies need them.”

If you feel terrible at first when you cut carbs and boost other macros, that’s normal, she says.

It’s “how we respond when our diet has drastically changed. When we change our diets, our bodies need time to process that change.”

The first few days of healthy eating can throw your body for a loop.

Some low-carb diets can cause fatigue and muscle soreness for up to two weeks. These changes can likely be attributed to the shift in your fuel source.

How to Feel Better

Before you make any big change to your diet, be sure to talk to a qualified healthcare provider, such as a registered dietitian or your doctor.

Those symptoms you’re feeling are your body’s way of getting your attention.

Tucker suggests really tuning in and listening. Consider whether your changes are sustainable and helpful or too strict.

Whenever a lifestyle or diet “becomes so strenuous that you are miserable following it, you’ll go right back to how you ate before,” she says.