Low-carb and keto
& how to cure them
Are you struggling while starting out on a low-carb or keto diet? Do you get headaches, leg cramps, constipation or any of the other more common side effects? Use the information on this page to avoid them – and feel great while losing weight.
Use one of the shortcuts below for a specific problem – or just continue reading for all of them.
Top 7 common problems when starting
Less common issues on low carb
Induction flu: headaches, lethargy, nausea, confusion, brain fog, irritability
The most common side effect on low carb is what’s known as “induction flu,” so called because it can mimic flu-like symptoms. It commonly occurs during the first week or two, often starting on days 2 through 4.
Symptoms include headaches, feeling tired, lack of motivation, nausea and lethargy. It’s also possible to experience confusion or “brain fog.”3
The good news is that these symptoms often disappear spontaneously within a few days or at most a couple of weeks.
The even better news is that you can possibly avoid these symptoms altogether by consuming adequate water, salt, and calories on day 1.4 It is presumed that the main cause is usually dehydration and/or salt deficiency, caused by a temporary increase in urine salt loss. Therefore, it makes sense that paying attention to hydration and electrolytes can help prevent it from occurring.
The cure: water & salt
You can potentially prevent – or at least minimize – many side effects by adding enough water and salt to replace what you lose when beginning a keto or low-carb diet.5
For example, increase your sodium intake by drinking a glass of water with half a teaspoon of salt. This may reduce or eliminate induction flu symptoms within 15-30 minutes. If so, this may be repeated once or twice daily, as needed, during the first week.
A better-tasting option is to use bouillon or broth (chicken, beef, vegetable, or bone broth).
In addition to sodium, make sure you’re getting enough of two other important electrolytes, magnesium and potassium.
The bonus: more fat
When beginning a keto or low-carb diet, make sure to eat enough protein and fat.6Eating a diet that’s low in both fat and carbs can be a recipe for feeling hungry, tired, and deprived.7 Low-carb diets should help you reduce your hunger, not increase it. A proper low-carb diet contains enough protein and fat to help you feel satiated and energetic.8 This can help speed up the transition time and minimize side effects.
If adding salt, water, and enough calories doesn’t completely eliminate the induction flu, do your best to stick with it a bit longer. Any remaining symptoms are likely to improve within days, as your body adapts to low carb and begins using fat as its main fuel.
If necessary, it’s of course possible to include more carbs in order to create a more gradual transition to low carb. While this may slow down the process and can result in slower weight loss, it may be a more viable long-term solution for many people.9
Leg cramps are not uncommon when starting a strict low-carb diet. It’s usually a minor issue if it occurs, but it can sometimes be painful.10 It’s unknown exactly why leg cramps occur, but they may possibly be due to the loss of minerals, specifically magnesium.
Here’s how to avoid leg cramps:
- Drink plenty of fluid and get enough salt. This may help prevent leg cramps.11
- If needed, supplement with magnesium. Here’s a suggested dosage from the book The Art and Science of Low Carbohydrate Living by Drs. Jeff Volek and Stephen Phinney: Take 3 slow-release magnesium tablets like Slow-Mag12 or Mag 64 a day for 20 days, then continue taking 1 tablet a day afterwards.13
- If the steps above are not enough and the problem is bothersome, consider increasing your carb intake somewhat. This may eliminate the problem, although it may reduce the impact of the low-carb diet.
For even more information and tips, check out our full guide: Guide Here are the six key things to know to kick your leg cramps to the curb, in our full leg cramps guide.
Six ways to kick nasty leg cramps to the curb
Guide Here are the six key things to know to kick your leg cramps to the curb, in our full leg cramps guide.
Constipation is another possible side effect, especially when first starting a low-carb diet, as your digestive system may need time to adapt.14
Here are the three steps to cure it, and you may only need the first one:
- Drink plenty of fluid and get enough salt. One common cause of constipation on low carb may be dehydration.15 This results in the body absorbing more water from the colon, so the colon’s contents get drier and harder, leading to constipation. The solution? Drink plenty of water and perhaps add some extra salt.16
- Eat plenty of vegetables or another source of fiber. Getting enough dietary fiber keeps the intestines moving, which may reduce the risk of constipation. Some may find their fiber intake decreases when eating low carb. However, eating plenty of non-starchy vegetables plus some nuts may help solve this problem. Another option for adding fiber to the diet that’s nearly carb-free is psyllium seed husks (mixed with plenty of water) or ground flaxseed.17
- If the steps above are not enough, consider trying 2 to 4 tablespoons (30-60 ml) of Milk of Magnesia (magnesium hydroxide) to relieve constipation.1819
For more on constipation, check out the guide below. Guide Are you constipated since going low carb or keto? This guide will explain all-things related to constipation and low carb.
What to do about constipation on a low-carb or keto diet
Guide Are you constipated since going low carb or keto? This guide will explain all-things related to constipation and low carb.
On a strict low-carb diet some people experience a characteristic odor of the breath. It’s often described as a strong, fruity smell, reminiscent of nail polish remover.
Higher levels of acetone can also lead to changes in body odor, especially when working out and sweating a lot.
Not everyone eating a ketogenic low-carb diet experiences this ketone breath – and for most people who do, it’s a temporary thing that often goes away after a week or two.22
For some people, it does not go away, though, and can remain a problem. Here are some possible solutions. The first two are more general, while the next three are more specifically targeted to the keto odor.
- Drink enough fluid and get enough salt. If your mouth feels dry – and it often can when starting a strict low-carb diet and entering ketosis – this means you have less saliva to wash away bacteria. This can result in bad breath, so make sure to drink enough.
- Maintain good oral hygiene. Brushing your teeth twice a day won’t stop the fruity keto smell (which comes from your lungs), but at least it won’t be mixing with other odors.
- Use a breath freshener regularly. This can mask the keto smell.
- Wait another week or two and hope that it resolves. Clinical experience shows that this is usually a self-limiting side effect.23
- Reduce the degree of ketosis. If the smell is a long-term problem and you want to get rid of it, one solution is to get out of ketosis or greatly reduce the degree of ketosis. This means including a few more carbs in your diet. Eating 50-70 grams per day may be enough to get out of ketosis.24 Of course, this will likely reduce the effectiveness of the low-carb diet when it comes to weight loss, diabetes control, and other health benefits; but, some people will find the more liberal diet to be powerful enough.
It’s common to experience a slightly elevated heart rate during the first few weeks on low carb, along with feeling as though the heart is beating a bit harder. This is normal and usually nothing to worry about as long as there aren’t associated symptoms of chest pain, weakness or feeling faint.25
As with many other side effects, one common cause may be dehydration and a lack of salt.
The quick solution to this problem is to drink enough fluids and make sure to get enough salt.
If adding salt and water does not completely eliminate heart palpitations, your symptoms might be related to stress hormones being released to maintain blood sugar levels (if you’re on diabetes medication, see the section below).26 This is often a temporary problem that occurs as the body adapts to a lower-carb diet, and will likely go away within a week or two.27
In the uncommon situation that the problem persists – and the palpitations are bothersome to you – try to slightly increase your carb intake. This will reduce the effect of the low-carb diet somewhat, so it’s a trade-off.
It’s possible that supplementing with magnesium may decrease palpitations, though the evidence is very weak.28 Taking up to 400 mg of magnesium per day (the recommended dietary allowance, or RDA) is safe for people with normal kidney function.
Important note if on medication for diabetes or high blood pressure
Decreasing carbohydrates decreases your need for medication to lower blood sugar. Taking the same dose of insulin or other diabetes medication as you did prior to adopting a low-carb diet might result in low blood sugar. One of the main symptoms of this is heart palpitations.
You should monitor your blood sugar frequently when starting a low-carb diet and work with your doctor to safely reduce your medication. If you are healthy or have diabetes that is treated either by diet alone or just with metformin, there is a very low risk of hypoglycemia.
If you need help finding a doctor knowledgeable about low-carb diets, you can consult our clinician map.
High blood pressure
On a low-carb diet, elevated blood pressure tends to improve or normalize for most people.29 This can reduce the need for medication and your dosage may become too strong, leading to low blood pressure. One of the symptoms of this can be an increased pulse and heart palpitations. If you experience this, it’s wise to check your blood pressure and contact your doctor to discuss possibly reducing or discontinuing your blood pressure medication.
Reduced physical performance
In the first few weeks on a low-carb diet your physical performance can be severely reduced.30 There are two main reasons for this:
- Lack of fluid and salt. This cause of most early problems when starting low carb can really hinder physical performance. Drinking a large glass of water with half a teaspoon of salt or a glass of broth 30–60 minutes before exercising might make a difference in performance.31
- Adaptation to burning fat takes weeks. The second cause of reduced early performance isn’t as quickly fixed. It simply takes time for your body – including your muscles – to shift from burning sugar to burning primarily fat for energy.32 It can take weeks or even months. After the adaptation period, some may see significant benefits (see below).
Increasing physical performance on low carb
While transitioning to a low-carb, high-fat (LCHF) diet often reduces physical performance initially, it may provide several potential benefits long term.33
The benefits of a low-carb diet in sports may be more obvious in long-distance running and other endurance events. The body’s fat stores are significantly larger than its glycogen stores. This means that once fat-adapted, an athlete may be able to perform for long periods of time without needing much (if any) external energy. This frees the athlete from having to activate their gastrointestinal tract during activity and can minimize the risk of digestive issues.
Another benefit is the reduction of body fat that often occurs on low carb.34 This reduction in body-fat percentage with lightening of the body can be a bonus for many sports.
However, the evidence is mixed with respect to whether athletes benefit from going low carb. Two papers by Dr. Louise Burke showed a reduction in endurance race-walking performance after 3-4 weeks of keto eating.35 Questions remain regarding if the adaptation period was long enough, but suffice it to say that this is still an area of debate without a clear answer.
You can read more in our evidence-based guide on carb cycling.
Temporary hair lossTemporary hair loss can occur for many different reasons, including any big dietary change. This is especially common when severely restricting calories (e.g., starvation diets or meal replacements).36 But it can also occasionally happen on low-carb diets.37
If so, it usually begins 3 to 6 months after starting the new diet, at which point you’ll notice more hairs falling out when brushing.
The good news is that even if you should be so unfortunate, this is usually a temporary phenomenon. And it’s likely that only a very small portion of your hair will fall out. Most find that the thinning will rarely be noticeable to others.38
After a few months, all the hair follicles will start to grow new hair and get back to normal. Of course, if you have long hair this could take a year or even more.
To understand exactly what is happening it’s necessary to know the basics of how hair grows.
Each hair on your head usually grows for about 3 to 5 years at a time. After that it stops growing for up to 2 months. Then a new hair strand starts growing in the same hair follicle, pushing the old hair out.39
So although you’re losing hair every day, because the hair strands are unsynchronized, this is not so noticeable. You lose one hair and another starts growing, so you always have about the same number of hair strands on your scalp.
Stress and synchronized hair loss
If your body experiences significant stress, more hair strands than usual can enter the resting phase at the same time.40 This can happen for many reasons, including:
- Starvation, including calorie-restricted diets and meal replacements
- Unusually demanding exercise
- Breast feeding
- Nutrient deficiencies
- Psychological stress
- Any big diet change
As the new hair strands start growing a few months later, all these formerly resting hair strands will drop at almost the same time. This is called “telogen effluvium” (read more about it) and is relatively common.
What to do
If there was an obvious triggering factor 3 to 6 months before the problem started – such as giving birth or transitioning to a strict low-carb diet – you don’t have to do anything. The problem should be temporary.
As long as you eat a varied and nutritious low-carb diet, it’s unlikely that stopping low carb will speed up hair regrowth. And unfortunately, you can’t stop the hair loss from happening once it has started, as the resting hairs will still fall out.
It’s possible to order blood tests for nutrient deficiencies, but unless you are on a vegetarian or vegan diet (with no supplements of iron or vitamin B12) it’s unlikely that these tests will show anything remarkable.41 However, if you have prolonged hair loss despite consuming adequate calories, especially protein, and there is no other obvious reason, then you may want to check with your doctor to make sure there aren’t any rare medical conditions that may be causing the issue.
How to minimize the risk of hair loss when starting low carb
First, temporary hair loss is relatively rare after starting a low-carb diet.42
There are no studies about how to minimize this small risk, but it’s likely helpful to avoid drastic calorie restriction (i.e. such a low calorie intake as to be unsustainable long-term). In addition, focus on getting adequate protein and allow yourself to include the amount of fat that makes your food palatable.43
It may also be helpful to reduce other sources of stress during your first few weeks on low carb. Sleep well, be kind to yourself, and don’t start an intense exercise program at the same time (wait at least a couple of weeks).
First, the great news: A low-carb high-fat diet usually results in an improved lipid profile, suggesting a lower risk of heart disease:44
- New analysis: LCHF best for long-term weight and health markers
- New major study: a low-carb diet yet again best for both weight and health markers!
The typical effect of a low-carb diet is an increase in HDL cholesterol (often referred to as “good” cholesterol), and a reduction in triglycerides, indicating a potentially lower risk of heart disease. With respect to LDL cholesterol, the profile typically shifts toward fewer small, dense LDL particles.45
It has also been shown that low-carb diet advice may result in reduced signs of atherosclerosis and an overall reduction in cardiovascular risk.46
Potentially troubling cholesterol results
Much of the time, the rise in total and LDL cholesterol is so small that many studies do not even pick up on it. But for a significant minority of people, there can be worrying elevations of LDL and total cholesterol, beyond what can be considered normal.47 This potential risk is worth taking seriously. It can also be worth taking steps to correct it.
While there are theories that this could be physiologically appropriate and not dangerous, we do not have convincing data to prove safety. Therefore, we need to consider that even if the lipid profile is otherwise good – with high HDL and low triglycerides – it still may be unhealthy.48
What to do
If your LDL rises dramatically on a low-carb diet, there are a few things to consider doing:
- Stop drinking Bulletproof coffee (butter, coconut fat or MCT oil in coffee). Don’t drink large amounts of saturated fat when you’re not hungry. This alone may normalize cholesterol levels.49
- Only eat when hungry and consider adding intermittent fasting, which might reduce cholesterol levels.50
- Consider using more unsaturated fats, like olive oil, fatty fish and avocados. Whether it will improve your health is unknown, but it will probably lower your cholesterol.51
- If steps 1-3 are not enough: Consider whether you really need to be on a strict keto diet for health reasons. If a moderate or liberal low-carb diet can still work for you, it may also lower your cholesterol. Just remember to choose good unprocessed, high-fiber carb sources like vegetables, nuts, and seeds rather than wheat flour or refined sugar.
- Consult with your doctor: You should discuss with your healthcare provider if medication therapy is warranted.
For much more about low carb and cholesterol, see our full guide:
When cholesterol is high and especially for people with preexisting heart disease, statins (the most commonly prescribed class of cholesterol-lowering medications) are often discussed. These drugs have been shown to lower the risk of heart disease, especially for secondary prevention. As with all medications, there are potential side effects so each use-case needs to be individualized.
Discuss any change in medication with your doctor.
Low carb and alcohol tolerance
When eating a strict low-carb diet, people may need significantly less alcohol to get intoxicated.52 So be careful the first time you drink alcohol on low carb. Possibly, you’ll need half as many drinks as usual to get the same effect. Low carb may save you money at the bar.
Obviously, if you’re going to be driving, be extra careful. Don’t ever drink and drive, period.
For more, check out these guides about low-carb diets and alcohol:
Gout and low carb
- A low-carb diet is not necessarily high in meat – just moderate.53 However, low-carb diets that are high in meat are markedly different from a meat-heavy, standard American diet.54
- All low-carb diets should have negligible amounts of sugar and refined carbohydrate. This is critical because there is a growing body of evidence suggesting a strong association between sugar intake and the risk of gout. If this relationship eventually proves to be a causal one, then low-carb diets would be considered a therapeutic tool for reducing the risk of gout.55
- There is clinical evidence that the risk of gout likely goes down on low carb, at least over the long term.56
However, there may possibly be a slight increase in the risk of gout during the first few weeks on a strict low-carb diet.57
For more on what really causes gout and how to avoid it, check out our full guide:
It’s been known for decades that when insulin levels drop — as they do when carb intake is very low— the kidneys excrete more sodium and water, although the exact mechanism isn’t clear:
Nutrition X 2019: Effects of differing levels of carbohydrate restriction on the achievement of nutritional ketosis, mood, and symptoms of carbohydrate withdrawal in healthy adults: A randomized clinical trial [randomized trial; moderate evidence] ↩
This piece of advice is based on known physiologic mechanisms and the consistent experience of clinicians who recommend this strategy, as well as the experience of people following this advice. [weak evidence]
There’s also some support from a study in which participants who were advised to drink bouillon experienced only minor side effects shortly after starting a low-carb diet:
Nutrition & Metabolism 2008: The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus [randomized trial; moderate evidence] ↩
A low-carb diet can include natural fats, including saturated fat. Although the issue remains somewhat controversial, several systematic reviews of randomized controlled trials and large observational studies have failed to show a connection between eating saturated fat and increased heart disease risk:
That being said, if not losing weight or even gaining weight on a low-carb diet, it may be worth increasing protein and decreasing fat intake. ↩
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This recommendation is from Drs. Volek and Phinney, who have conducted dozens of trials in people following very-low-carb diets. However, the intervention itself has not been tested in scientific trials. Therefore it is ungraded evidence without clear scientific backing other than expert opinion [expert opinion; ungraded] ↩
In a study of people with type 2 diabetes who ate 20 or fewer grams of carbs per day, slightly more than half reported constipation at some point during the trial:
Nutrition & Metabolism 2008: The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus [randomized trial; moderate evidence]
When increasing fiber from any source, it is critical to ensure adequate fluid intake as well, because more fiber without adequate fluid can worsen constipation.
Clinical Nutrition ESPEN 2019: Effect of flaxseed or psyllium vs. placebo on management of constipation, weight, glycemia, and lipids: a randomized trial in constipated patients with type 2 diabetes [moderate evidence]
Taking a standard dose of magnesium hydroxide is considered safe for people with normal kidney function and can be expected to produce a bowel movement within several hours:
Diet Doctor will not benefit from your purchases. We do not show ads, use any affiliate links, sell products or take money from industry. Instead we’re funded by the people, via our optional membership. Learn more ↩
The three ketone bodies are acetone, acetoacetate, and beta-hydroxybutyrate. ↩
Breath ketone meters measure the amount of acetone in your breath in order to confirm that your body is burning fat and producing ketones:
Most studies on ketogenic diets limit carbs to less than 50 grams per day in order to promote nutritional ketosis:
Experienced clinicians have reported that patients are often unable to remain in ketosis when consistently eating more than 50 grams of carbs per day, although this may vary based on physical activity, fasting, and insulin sensitivity.[weak evidence]
In one study, increasing magnesium intake by 50% helped reduce the frequency of ventricular arrhythmias in people with frequent heart palpitations, but symptoms were equally reduced in the magnesium and placebo groups. This calls into question how effective magnesium truly is for symptom relief.
Journal of the American College of Cardiology 1997: Antiarrhythmic effects of increasing the daily intake of magnesium and potassium in patients with frequent ventricular arrhythmias [randomized trial; moderate evidence] ↩
This has been shown in several high-quality trials:
Nutrition Research 2019: Weight loss, improved physical performance, cognitive function, eating behavior, and metabolic profile in a three or four-week ketogenic diet in obese adults [non-randomized trial; weak evidence]
This has been shown in both obese people and athletes:
Sports 2018: The three-month effects of a ketogenic diet on body composition, blood parameters, and performance metrics in CrossFit trainees: a pilot study [non-randomized trial; weak evidence]
Journal of Physiology 2017: Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers [randomized trial; moderate evidence]
PLoS ONE 2020: Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible [randomized trial; moderate evidence]
Low-carb diets that contain both animal and plant foods typically provide adequate amounts of all vitamins and minerals:
In many low-carb studies showing health benefits, people are advised to eat an adequate amount of protein and as much fat as needed to feel satisfied:
Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]
Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study [nonrandomized study; weak evidence] ↩
Some studies suggest that smaller LDL particles are more correlated with heart risk compared to larger LDL particles:
Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study [non-controlled study; weak evidence] ↩
In studies, some people eating low-carb diets have experienced a 30-44% increase in LDL cholesterol:
In addition, a small subgroup of people can end up with total cholesterol numbers over 400 mg/dl (10 mmol/l) on a strict low-carb diet, and LDL numbers over 250 mg/dl (6.5 mmol/l). This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence]. ↩
As of September 2021, there are no studies specifically looking at “hyper-responders,” the people whose total and LDL cholesterol rises dramatically in response to a low-carb diet. While very high LDL levels have been consistently associated with an elevated risk of cardiovascular disease in the general population, there are reasons (outside the scope of this guide) to question whether all hyper-responders have this high risk.
In the absence of clear evidence that it is safe for people eating low carb to have very high LDL, we strongly recommend that hyper-responders consult with their physicians, preferably physicians with experience in the realm of how low carb can affect lipids. ↩
Consuming a lot of saturated fat has been shown to increase the number of LDL particles in some people:
The American Journal of Clinical Nutrition: Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults [randomized trial; moderate evidence]
A study in people with metabolic syndrome found that consuming fish oil and olive oil for 3 months significantly lowered their LDL cholesterol levels:
This is commonly reported by people on a keto diet. However, there isn’t much scientific research yet to explain why tolerance seems to be reduced, just hypotheses:
Very low-carb diets studied in the literature usually include less than 30 grams of carbohydrates per day, while moderate to liberal low-carb trials may include up to 50 or 100 grams of carbs, respectively.
On the other hand, observational studies of the standard American diet estimate an average intake of 250 grams of total carbs/day, with 210 grams of that considered “low quality.”
Observational studies have found an association between sugar intake and risk of gout. More evidence is needed to show a cause and effect relationship.
BMJ Open 2016: Fructose intake and risk of gout and hyperuricemia: a systematic review and meta-analysis of prospective cohort studies [meta-analysis of nutritional epidemiology studies; very weak evidence]
In a randomized trial of people who ate a high-protein, low-carb diet for six months, uric acid levels declined, especially in those who were obese:
This RCT showed that a low-carb diet led to the same amount of uric acid reduction as did a low-fat or Mediterranean diet:
Diabetes Care 2000: Effects of Low-Fat, Mediterranean, or Low-Carbohydrate Weight Loss Diets on Serum Urate and Cardiometabolic Risk Factors: A Secondary Analysis of the Dietary Intervention Randomized Controlled Trial (DIRECT) [randomized trial; moderate evidence]
There’s also some interesting early research suggesting that a ketogenic diet may help reduce gout flares, although much more study is needed:
In the following nonrandomized study, a 30% protein diet led to lower uric acid levels and fewer gout attacks:
Annals of Rheumatologic Diseases 2000: Beneficial effects of weight loss associated with moderate calorie/carbohydrate restriction, and increased proportional intake of protein and unsaturated fat on serum urate and lipoprotein levels in gout: a pilot study [nonrandomized study, weak evidence]
Most studies have found no differences in uric acid levels among people on low-carb diets vs. low-fat or control diets:
Diabetes Metabolism Research & Reviews 2018: Effect of low-carbohydrate diet on markers of renal function in patients with type 2 diabetes: a meta-analysis
[systematic review of randomized trials; strong evidence]
Yet some low-carb researchers and clinicians have reported that some people who start eating low-carb diets experience an initial temporary rise in uric acid levels that could slightly increase gout risk. [weak evidence]