Why Healthy Eating Can Cause Bloating, Headaches, and Fatigue

Healthy Eating Can Feel Worse at First

Interviewer: Sometimes when you start eating healthier, you feel worse at first. Today, common negative reactions, which are short-term, to eating healthier. Is it normal when someone goes from not eating to eating healthy to feel some negative side effects?

Staci McIntosh: It depends on where you're coming from and where you're going. What did you eat before, and how much did you change that? The more you change your diet, the more adjustment time will be necessary

Interviewer: How about from not too healthy to really healthy?

Staci McIntosh: Expect a couple of weeks. It's going to take some adjustment for sure.

Gut Bacteria Changes Can Cause Gas and Bloating

Interviewer: What about some specific symptoms?

Staci McIntosh: So a lot of times our gut is populated with bacteria . . . Well, it's always populated with bacteria, and it gets specific to the types of foods that we're eating. When you change that, and you're eating more fruits or vegetables, then the type of bacteria that populates your gut is going to change with it, and that takes an adjustment period, and that will result in gas, bloating, and a change in the population of that bacteria.

Interviewer: If you already said this, I'm sorry, but the bacteria probably helps you digest, and you need to get the right kind for the food.

Staci McIntosh: Exactly, we all have bacteria in our gut, and it's part of our happy gut flora, and there's a healthy population of a variety of bacteria, and then there's not so much of a healthy population.

Interviewer: So you've got to get rid of the fast food bacteria and get some fresh fruit bacteria in there?

Staci McIntosh: You're introducing the good bacteria as you eat more fruits and vegetables, and then that's going to start changing the whole flora.

Fiber, Water, and Why Constipation Happens

Interviewer: What about constipation and diarrhea is that the same thing going on there?

Staci McIntosh: Some of it will be. Some of it may be that you've gone from a low-fiber diet to a pretty high-fiber diet without a transition period, and without enough water during that time. So I always recommend that if someone's going from a pretty low-fiber diet, the average American eats 13 grams of fiber a day, and the average recommendation is between 25 and 38 grams a day.

Interviewer: Wow, so almost half.

Staci McIntosh: So we're a pretty low-fiber community in general, so if we're going from a low-fiber diet to a high-fiber diet, we need a little transition period, and we need to increase the amount of water and activity that we're doing so that it helps get things healthy and not result in constipation.

Interviewer: Is that another enzyme issue?

Staci McIntosh: It's not an enzyme issue. Because we don't digest fiber, so there's no enzyme to digest fiber, but it's just a matter of the fiber sucking in water, and that's what helps make an easier stool to pass, but if you don't have the extra water for it to suck in, then it becomes constipation.

Can Eating Too Few Carbs Cause Brain Fog?

Interviewer: All right, what about like brain fog? I feel like when I start my new diet sometimes I get brain fog. I'm not as sharp as I used to be. What could be going on there?

Staci McIntosh: You know, I would have to find out more about what you were eating before and then what you changed to. I would expect, I expect to hear those kinds of questions sometimes when I have a patient who's going to a low-carbohydrate diet, or going to a paleo diet, or going to some extreme diet where they don't have enough carbohydrate intake, and then it will make you feel like a brain fog because you don't have enough basic glucose in the brain.

Interviewer: So you can eliminate too many carbohydrates?

Staci McIntosh: Absolutely.

Why You May Feel Tired on a New Diet

Interviewer: What about fatigue and low energy is that a carbohydrate issue again?

Staci McIntosh: Yeah, your basic, your primary source of fuel for every cell in the body is glucose.

Interviewer: Could it be just more calories could be the solution for something like that, or does it need to be carbs?

Staci McIntosh: It needs to be glucose. You're going to use glucose for your brain; you're going to use glucose for energy for every cell in the body, and you can get that glucose from breaking down glycerol from fatty acids, or from turning amino acids into glucose, but that's just another step that your body has to go through.

Interviewer: Got you.

Staci McIntosh: So if it has available glucose, then you have available energy for the cells.

Common Causes of Diet-Related Headaches

Interviewer: What about headaches? What could cause that if you're changing from one philosophy of eating to another?

Staci McIntosh: A lot of different things. So sometimes if people are going into using a lot of non-nutritive sugar replacements, saccharin, aspartame, all those types of things. If you would normally drink soda and then you go to a diet soda that can give people headaches a lot of times, and also if you're going to a really low carbohydrate diet your brain uses glucose, and every cell in your brain uses glucose, and it wants glucose, and if you don't have enough glucose available if you're on either a very low-calorie diet, you're not getting enough fluids, or you're not getting enough glucose regardless of the calorie amount that would be a typical recipe for a headache.

Healthy Eating Can Trigger Cravings

Interviewer: Okay, how about extreme cravings? Now all of a sudden I want everything that's not good for me anymore.

Staci McIntosh: That's human nature.

Interviewer: Is that what that is?

Staci McIntosh: Yeah, that's human nature. As soon as you say you can never have chocolate again, that's all you're going to think about.

Interviewer: Yeah, so that's why it's probably good to maybe allow yourself a little.

Staci McIntosh: That's why everything in moderation.

Are Sugar and Caffeine Withdrawal Symptoms Real?

Interviewer: A little taste, all right. What about going through withdrawals of things like caffeine, or sugar, are there withdrawal symptoms to those types of things?

Staci McIntosh: Absolutely, when you look at someone's MRI scan, for example, and you look at the result that it has on the brain for sugar versus nicotine, it's the same area of the brain that gets stimulated so it does trigger, certainly not an addiction like nicotine would, but it's triggering the same areas of the brain so you can experience those withdrawals.

Interviewer: All right, and some headaches might be caused by getting rid of the bad stuff, and you're actually going through withdrawals, like . . . wow.

Staci McIntosh: Sure.

The Best Way to Transition to a Healthier Diet

Interviewer: When somebody goes on a new diet, what words of advice do you have for them to get through this process? I imagine some of these things actually stop people from eating better.

Staci McIntosh: Absolutely, I say one step at a time; don't change everything overnight. If you have gained excess weight, you gained it one gram at a time. Let's think about losing it one gram at a time, not changing everything all at once, and keeping in mind that eating is a basic enjoyment of life. If you're changing to a diet that is really not that enjoyable, then why do that? Why not just start on something that you plan to do the rest of your life because it's healthy, and it's enjoyable, and you and your entire family can do it?

_{updated: July 23, 2026
originally published: February 26, 2014}