Low-Carb Diet Contraindications

Low-carb diets, such as ketogenic diets, have become popular for helping with weight loss and some medical conditions like epilepsy and Type 2 diabetes. However, they are not suitable for everyone. For certain people, starting a low-carb diet can lead to serious health problems. Knowing when a low-carb diet is unsafe helps prevent these problems and protects your overall health.

Changing from a regular diet to a low-carb one means the body switches from using carbohydrates for energy to using fat, creating substances called ketones. While this process usually works well for many people, some health conditions can make this switch dangerous. This article explains when low-carb diets may be unsafe or need extra care, and why it’s important to get advice from a doctor before starting.

Who Should Avoid or Be Careful With Low Carb Diets?

Choosing a low-carb diet affects how your body handles food and energy, so it is important to think about your own health situation before making this change. Some people are at a higher risk if they eat very few carbohydrates, and these risks depend on their medical history and current health.

Below, you’ll find a breakdown of two types of situations:

• Absolute contraindications: People in these groups should not follow a low-carb diet, as it is generally unsafe for them.
• Relative contraindications: In these cases, the diet may be possible but requires careful supervision by a health professional.

Each person responds differently, even with similar backgrounds, so advice from your doctor is always best.

Absolute vs. Relative Contraindications

Medical Situations Where Low Carb Diets Can Be Harmful

For some people, eating very few carbohydrates can make medical problems worse or create new ones. The list below shows some main medical reasons to be careful or to avoid low-carb diets.

• Liver Failure: People with severe liver problems cannot safely process fats and ketones, so a low-carb or keto diet could cause more liver damage or mental confusion. Only a liver specialist can decide if this diet is ever an option-and usually, it’s avoided.
• Chronic Kidney Disease: Mild cases may be okay with close medical checks, but advanced kidney disease makes it harder to get rid of acids from ketosis. This can lead to dangerous blood changes, so a kidney doctor must assess anyone with kidney issues.
• Type 1 Diabetes: These individuals have a higher risk for serious conditions like diabetic ketoacidosis (DKA) and low blood sugar. Only under strict medical monitoring should a Type 1 diabetic try a low-carb diet, and only in special cases.
• Using SGLT-2 Inhibitors: People taking these diabetes medications should not use a low-carb or ketogenic diet. The combination may cause a dangerous condition called “euglycemic DKA,” which can be deadly.
• Pregnancy and Breastfeeding: Eating very few carbohydrates during pregnancy or nursing may harm the baby or mother and can cause rare but serious problems. Pregnant and breastfeeding women generally should avoid keto diets.
• Heart Rhythm Problems: Individuals with abnormal heart rhythms need caution. Some very low-calorie, low-carb diets in the past caused fatal problems, though carefully planned versions today are safer. Doctors should check the heart before starting.
• Recent Heart Attack or Stroke: There is not enough good research to know if these diets are safe after such an event. Until there’s more information, people recently hospitalized for heart attack or stroke should avoid low-carb diets.
• Severe Heart Failure: For those with serious heart failure, ketone-based diets may cause further problems with fluid and minerals in the body. Heart doctors should be involved in all decisions.
• Breathing Failure: The research is unclear here, but ketosis can add to acid buildup. People who have serious lung disease should only try low-carb diets if a lung specialist agrees.
• Active or Severe Infections: The body’s healing may slow down on a low-carb diet during big or ongoing infections. More study is needed, but most healthcare providers suggest regular eating until you recover.
• Eating Disorders or Substance Abuse History: For those with past or current eating disorders, low-carb diets can worsen unhealthy eating behaviors or trigger a relapse. The same goes for substance abuse, which can increase dangerous acid build-up.
• Frail Older Adults: Elderly people who are weak, or have trouble remembering things, risk dehydration, low blood pressure, and mineral shortages on strict low-carb diets.
• Surgical Patients: Before and after surgery, the body needs glucose to handle stress and heal. Staying on a strict low-carb diet during this time can create problems, so most use regular diets around surgery time.
• Cancer: Research is ongoing about ketogenic diets in cancer. Some cancers may respond well to a keto diet, but it can be harmful in others like melanoma or kidney cancer. Anyone with cancer should only make dietary changes under their doctor’s care.
• Gout or Abnormal Cholesterol: Sometimes, a low-carb diet can cause a short-term rise in uric acid or worsen cholesterol-especially in lean people or those using ketogenic diets for epilepsy. Labs should be checked regularly.
• Genetic/Fatty Acid Metabolism Disorders: Certain inherited problems mean the body cannot handle fats and ketones, so low-carb or keto diets can cause severe low blood sugar or even life-threatening results. These conditions are rare and are usually found early in life.

Other Groups That Need to Be Extra Careful

Some people have special needs or challenges that mean they need extra supervision if they try a low-carb diet, even if they do not have the specific medical problems listed above.

• Children and Teens: Unless being used for conditions like epilepsy under close doctor’s care, kids and teens shouldn’t use low-carb diets for weight loss or general health, as they need nutrients for growth and development.
• Older Adults: Aging changes body chemistry and can raise the risk of medication problems, falls, and mineral shortages. Extra care is needed if older adults choose this diet, especially if they have multiple health concerns.
• Athletes and Active People: Sports and intense exercise often require higher carbohydrate intake for best performance and energy. Without careful planning, a low-carb diet can lower stamina, slow recovery, and cause injuries.

Possible Risks and Side Effects of Low Carb Diets

Even healthy people may run into problems when following a strict low-carb or ketogenic diet. Below are some common risks and complications:

• Ketoacidosis: Normal ketosis is safe for most, but certain people (such as those with diabetes or who use SGLT-2 inhibitors) may slip into a dangerous form of this called ketoacidosis. If you have a history of this, you should avoid strict low-carb diets.
• Electrolyte Loss and Dehydration: Dropping carbs suddenly can bring on the “keto flu,” with headaches, tiredness, and dizziness. This is because the body loses water and important minerals like sodium, potassium, and magnesium. Drinking more fluids and replacing minerals can help, but symptoms that are strong or do not go away should be reported to your doctor.
• Hypoglycemia in Medication Users: If you use insulin or diabetes pills, a low-carb diet can drop blood sugar too low. Medication doses often need to be changed, and you may need more frequent blood sugar checks.
• Heart Concerns: While some heart markers may improve, LDL (“bad” cholesterol) can go up for some people. Mineral shortages can also affect the heart rhythm. If you have heart disease, have your cholesterol and heart monitored by your doctor.
• Mental Health: The strict nature of low-carb diets may cause anxiety, depression, or worsening of eating disorders in some people. Some feel better mentally, while others feel worse. Anyone with a prior mental health condition should be careful and consider speaking to a mental health professional before starting.

Questions to Ask Your Healthcare Provider Before Starting

Talking to your doctor before you start is always the best plan, especially if you take medications or have any medical problems. Here are some checks your healthcare provider may want you to have:

• Physical exam and blood work, including kidney and liver function, minerals, and glucose
• Cholesterol and triglyceride (lipid) panel
• HbA1c for those with diabetes
• Heart rhythm test (EKG), especially if you have a heart history or plan a very low-calorie diet

Let your doctor know about any previous or current illnesses, all your medications, and family history. This helps them decide if a low-carb diet is safe for you and what you should watch out for.

When to Stop the Diet

It’s important to recognize signs that a low-carb diet may be causing harm:

• Severe or long-lasting “keto flu” symptoms (like extreme tiredness, dizziness, or nausea)
• Heart palpitations, serious muscle cramps, or confusion (all possible signs of mineral problems)
• Frequent or bad low blood sugar episodes if you use diabetes medications
• Signs of kidney or liver problems (swelling, dark urine, yellow skin/eyes)
• Ongoing weight loss that seems abnormal or doesn’t stop
• Sharp and lasting rise in LDL cholesterol
• Any new or worrying symptoms

If any of these problems show up, speak with your doctor right away and ask if you should stop or change your diet. Always follow their guidance for what to do in these situations.