While it seemed trendy in the beginning, the low-carb craze seems to be sticking around as people following the keto diet continue to share their #progresspics all over social media. While some of these weight loss stories are pretty impressive, going low-carb can have some negative effects on your health—especially on diets like keto where the percentage of carbs goes as low as 5 % of your daily calories.
The 2020-2025 Dietary Guidelines for Americans advise getting 45-65% of our daily calories from carbs. Opting for 40% or less can have a major impact on the way your body functions. Carbs are our body's fuel for metabolism, energy, digestion and many other important activities, and eating too few could be consequential.
"Since lots of people think about carbs in terms of grams, anything lower than 100 grams daily is pretty low," says Lisa Valente, M.S., R.D. "And since carbs have 4 calories per gram, that would be 400 calories, or only 20% of your daily calories on a 2,000-calorie diet."
If you're on a low-carb diet, here are some signs and symptoms of eating too few carbs that you'll want to take notice of.
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1. You're Always Tired
Since we've established that carbohydrates are the primary source of fuel for our body, slashing your intake could have a major impact on your energy level. Carbs are converted to energy more efficiently than protein or fat, so you may start feeling a little sluggish throughout the day on a low-carb diet. Weakness and fatigue—sometimes called "keto flu"—are common side effects of a low-carb diet, according to a 2020 study in Frontiers in Nutrition.
According to a 2023 review in Physical Activity and Nutrition, this can also have a negative impact on your workouts, as you may not feel like you have the strength to push through a sweat session like you used to. It may be worth upping your carb intake a little bit to ensure you have the ability to make it through each day—and your exercise regimen.
2. The Bloating Is Real
Carbs often get a bad rap for causing bloat, but for many, that temporary bulge might be caused by eating too much refined sugar or white flour. Reducing your carbohydrate intake often means reducing the amount of fiber you eat in a day, as fiber is most concentrated in carbohydrate-rich foods such as whole grains, fruit and vegetables (although eating too much fiber can also cause bloat).
Because fiber keeps things moving through your gut—and out your body—not eating enough of it can cause constipation. And when things are backed up, it can cause some major gas and bloating.
When going low-carb, it's imperative to ensure the carbohydrates you are eating are high-quality. Simply swapping your white bread for whole-wheat or adding a handful of berries alongside your morning omelet could make a huge difference in reducing your bloat.
3. It's Becoming Difficult to Concentrate at Work
Following a low-carb diet can reduce your energy levels, impair your concentration and even make you feel grouchier than normal (sounds like a blast!)
High-quality carbs like sweet potatoes, whole-wheat bread, berries and quinoa are essential for not only giving you the energy you need to get through your workday, but their protein-fiber combo helps to lower blood sugar spikes and prevent you from crashing.
Instead of reaching for yet another cup of coffee at 2 p.m., it might be worth strategizing your carbohydrate intake to allow for a little high-fiber afternoon snack.
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Pictured recipe: Shrimp Scampi Zoodles
4. The Scale Is Starting to Creep Up
If you're on a low-carb diet to lose weight, you expect the scale to be going down. Ironically, though, diets that are too low in carbs can have the opposite effect over time as your body may react to the decreased carbohydrate intake by trying to produce its own usable glucose from protein or fat. As this continues, your body may start to store this sugar as fat to "prevent starvation," as the brain doesn't differentiate between true starvation and purposely reducing calories or carbohydrates.
To be fair, research is mixed. For example, the same 2023 review in Physical Activity and Nutrition suggests that the keto diet has been shown to effectively reduce belly fat and maintain muscle mass—at least for the short term. And if you've got the energy to strength train while on keto, and are adding muscle mass, the number on the scale may go up some, even though your body composition may be improving.
With that said, like any other diet, after you stop it, chances are any weight you lost will return—unless you make and stick to realistic sustainable changes. And not only that, but any kind of restrictive diet is likely to lead to cravings, which can lead to binging.
Reconsider your weight loss efforts if you're becoming too tired to exercise—which has a host of benefits beyond weight loss—and have lots of cravings, as it will likely cause the scale to go up and won't be sustainable for the long haul.
5. You Don't Feel Satisfied for Long After a Meal
Complex carbohydrates can help suppress your appetite, as they assist in regulating your hunger and fullness cues. Our bodies need fiber to bulk up and help slow down the digestion process—which allows us to feel full longer. But it's difficult to get enough fiber when cutting carbs.
Going low-carb can also put you at risk for nutrient deficiencies. This, too, can throw your hunger and fullness cues out of whack—not to mention weaken your immune system since many necessary vitamins, minerals and antioxidants are in carbs that might not be "allowed" on certain low-carb diets.
Research, like a 2022 study in Nutrients, suggests that those who consumed more fiber felt fuller and had smaller appetites compared to those who ate less fiber. As with anything, though, not everyone experiences this, as a 2023 study in Nutrients suggests no difference in appetite between people eating high-fiber and those who didn't.
It's important to note that eating carbs by themselves—whether high fiber or not—does not offer lasting fullness like eating carbs with fat or protein does. So combine your carbs with healthy fat—like avocado or peanut butter—or protein—like cheese or nuts—to get longer-lasting, stable energy and fullness.
6. Your Poop Habits Are Off
We keep coming back to this whole "fiber" thing because it's important. As we already mentioned, a side effect of low-carb diets—especially ketogenic diets—is constipation. Our bodies are missing out on fibrous, hydrating foods when we slash our carbohydrate intake, and both fiber and water are essential for regular digestion. This is not only annoying but can also lead to bloating, diarrhea and other GI issues down the road.
Veggies are an important food source for anyone trying to eat healthily, but they are even more crucial for those following a low-carb diet. Try upping your intake of your favorite veggies as well as adding some fresh fruit and whole grains into your daily eating regimen to keep things moving.
7. Your Breath Reeks
People following a keto diet have an extra-long list of potential consequences, one of them being some seriously bad breath. When your body goes into ketosis and stops using carbohydrates as fuel—switching to fat instead—it produces acetone, which starts to build up in the body and is responsible for the stink.
If you're experiencing chronic bad breath, it may be a sign your body needs some carbs. The vast majority of health professionals agree that unless you are under a very specific circ*mstance, the keto diet should not be a long-term eating pattern.
The Bottom Line
"When you cut out carbs, you're not just cutting out soda and cake," says Valente. "You lose fruits, whole grains and lots of vegetables, which all deliver fiber but also vitamins, minerals and antioxidants to your diet. These can be hard to make up for on a low-carb diet."
While achieving a balanced diet is certainly easier said than done, it's important to eat from every food group for optimal health. There is so much more to your health than the number on the scale, and weight loss should be done to protect your health.
If you do decide to go low-carb, it's important to ensure you're getting enough fiber each day, prioritizing healthful carbohydrate sources when possible. It's also vital to make sure most of your fat intake comes from omega-3's, mono- and polyunsaturated fats to properly fuel your body.
Check out our Low-Carb Diet Center for tips, recipes and resources to help you get started on a nourishing eating plan that doesn't leave you with any of the negative side effects of going too low on carbs.
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