Low-Carb Diet and Diarrhea

Lowering your carb intake might give you an edge on weight loss — at least in the beginning. But first, you have to get over the hurdles that such a big diet change can throw in your path. Low-carb diet side effects, including diarrhea, can be bothersome as your body adapts to the diet; in some cases, they may persist beyond the introductory period.

The beginning of a low carb diet can be difficult. (Image: barol16/iStock/GettyImages)

Diet Changes and Digestion

Any time you make a change to your eating habits, you risk disrupting your digestive system's homeostasis — or balance. Taking away foods and nutrients your body is used to relying on or adding new ones can throw your gastrointestinal, or GI, system for a loop — and it may let you know in more ways than one.

Suddenly cutting your carb intake is bound to have at least some effect on your digestion. It may improve your digestion if you used to eat a lot of refined grains and sugary junk foods or if you're one of those people who are sensitive or intolerant to certain types of carbs. But if that's the case, you're probably not reading this article — because you feel great right now.

If that's not you, then rest assured you are not alone. Most people who cut carbs experience some low-carb diet side effects — and those who cut carbs drastically experience more.

A common result of eating fewer carbs is constipation. Carbs are a rich source of dietary fiber, which adds bulk to stool and softens it so it's easier to pass. Eating less fiber will have the opposite effect. But, according to the Mayo Clinic, diarrhea is also a common side effect of low-carb diets. This is likely due to the foods you have added to your diet to replace the carbs you have cut.

Keto Diarrhea From Fat Intake

The ketogenic diet is an extreme low-carb diet that cuts carbs to a maximum of 50 grams daily, but often much less than that. In addition, fat intake is increased to as much as 90 percent of calories, according to Harvard Health Publishing. That is a whole lot of fat for your digestive system to have to deal with suddenly.

Even in normal amounts, fat is harder for the body to digest than protein, starches or sugars. Of the three macronutrients, fat takes the longest to digest, which can put more stress on your GI system and cause diarrhea, gas, bloating and other uncomfortable symptoms. People with digestive disorders are often encouraged to lower their fat intake because of this.

In fact, according to an October 2016 article published in the World Journal of Gastroenterology, a high-fat diet can disrupt the microbiome — the population of beneficial bacteria in your gut that regulates digestive health. This is especially true of increased ingestion of saturated fats from meat and dairy products. The authors report a link between high fat intake and digestive disorders such as Crohn's disease and ulcerative colitis.

Last, some people have more trouble than others digesting fat. When your body can't digest and absorb fats normally, they are broken down in the colon into fatty acids, Harvard Medical School professor Dr. Norton Greenberger told Harvard Health Publishing. This causes the colon to secrete fluids, which can trigger diarrhea.

Problems With Protein and Dairy

An increase in protein can also cause digestive distress for some people. The keto diet keeps protein intake at a moderate level — about 35 percent, according to an article published online in StatPearls in January 2019. This is at the high end of the range of 10 to 35 percent of calories recommended for the general population by the National Academy of Medicine. But, unless your protein intake was previously very low, this amount isn't likely to cause problems.

However, if you are choosing to follow a low-carb, high protein and low- to moderate-fat diet, rather than a high-fat keto diet, a large increase in protein can be problematic, causing either constipation on diarrhea, reports Harvard Health Publishing. Like fat, protein is also harder for the body to digest; it has to work harder to break down the macronutrient into its constituent amino acids.

This is the benefit of a high-protein diet for weight loss. Not only does protein stay in the stomach longer than carbohydrates, but it also takes a lot of energy for your body to digest, increasing your metabolism during digestion by up to 30 percent, according to an article published in Nutrition & Metabolism in November 2014. However, eating a lot of protein at once can stress the digestive system and lead to stomach upset.

A high-protein or high-fat diet may also include increased amounts of dairy. For people who have trouble digesting the milk sugar lactose, this can cause a host of problems, including diarrhea. Using a protein supplement can be a good way to boost your protein intake; however, you may be sensitive to some types of protein more than others. Whey protein is a common culprit because it contains lactose.

Effects of Sugar Substitutes

Having a sweet tooth on a low-carb diet can be excruciating. This causes many people to turn to sugar substitutes, such as erythritol, xylitol, sucralose and stevia. These sweeteners have no calories and no effect on blood sugar, and many people go overboard because of this.

Some may find sugar substitutes cause no problems — whether or not they are actually good for them is another story. For other people, these sweeteners can have a laxative effect, especially when consumed in large amounts. This can leave you running for the bathroom right after indulging in your favorite treat, which isn't so sweet.

Is It Just Temporary?

The good news is that diarrhea and other low-carb diet side effects are often fleeting. They may last for a week or so while your body adjusts to the change. After that, you may find that your digestive system normalizes. But whenever you are making a diet change, it helps to do so gradually, so your body can take more time to adjust. This may prevent low-carb diet diarrhea altogether.

In other cases, for example, for those who are lactose intolerant, the diarrhea may persist. If you find that your new diet continues to cause digestive problems, it just may not be a good fit for you. Diarrhea that lasts longer than a few days is not only uncomfortable, but can also lead to dehydration and nutrient malabsorption. In this case, it's best to go back to your regular diet immediately and check in with your doctor.

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