What to Know About Medications and Low-Carb Diets

You've heard it a million times: "Before you start a new diet or exercise program, check with your doctor." Before starting a low-carb diet, it's important to discuss your plans with your doctor—especially if you are being treated for certain health conditions like diabetes and high blood pressure.

Why? When you make changes to what you eat, how much you eat, and when you eat, your medications may be affected. Additionally, many medications are formulated with a certain amount of carbohydrates included.

As long as your doctor is aware of the changes you intend to make, they can help ensure your medications remain safe and effective. The dosage of some medications may need to be changed, or your doctor may want you to take it at a different time of day.

Low-Carb Diets and Specific Conditions

If you have certain medical conditions, your doctor may suggest a low-carb diet to help control your symptoms or prevent the condition from getting worse. In some cases, a low-carb diet may even help reverse the condition.

Conditions Positively Affected by a Low-Carb Diet

In people who have these conditions, a low-carb diet may help (but always check with your doctor first):

• Obesity
• Type 1 and type 2 diabetes
• Elevated blood glucose or prediabetes
• Non-alcoholic fatty liver disease
• Metabolic syndromes (high cholesterol, high blood pressure)
• Glycogen storage disease
• Glucose transporter 1 (GLUT1) deficiency syndrome (a rare genetic condition)
• Conditions affecting the brain, including epilepsy, Parkinson's disease, and Alzheimer's disease

Some research explores whether low-carb or ketogenic diets may be beneficial for people with certain types of cancer. Several studies have investigated whether reducing insulin levels could help slow the growth of cancerous tumors or keep cancerous cells from spreading, with promising results demonstrated in animal studies.

More human studies are necessary to determine the efficacy of low-carb diets for cancer. Discuss the option of diet changes with your oncologist before adopting a low carb or ketogenic diet.

Conditions Negatively Affected by a Low-Carb Diet

In these cases, a low-carb diet may not be beneficial and may even be harmful. Ask your doctor before starting a low-carb diet if you:

• Are underweight or malnourished
• Have a history of disordered eating
• Are pregnant or nursing
• Are very physically active
• Are recovering from surgery, injury, or serious illness, or are immunocompromised
• Have chronic medical conditions affecting your heart, kidneys, or intestines, or other major organ systems

Diabetes Medications

If you're taking medication to treat diabetes, such as insulin, you're already aware of the direct relationship between carbohydrates in the food you eat and how much insulin your body needs.

It's imperative to notify your doctor of dietary changes if you're taking insulin. Major dietary changes need to be coordinated carefully with your physician and/or dietitian.

Insulin

Fewer carbs mean less insulin. The less carbohydrate you eat, the less variation in blood glucose your body will experience. For this reason, a low-carb diet may be suggested (even prescribed) if you have diabetes and are insulin-dependent.

When you eat more carbs, there will be more variation in your blood glucose levels. It can be tricky to know exact carb counts, even in fresh food. This makes adjusting for insulin sensitivity more of a challenge.

For example, a cup of cauliflower has about 5 grams of carbohydrate, but the nutritional information for fruits and veggies is based on averages. You won't know exactly how many carbs are in the specific cauliflower you're holding, but you can make an estimated guess.

However, compare the approximate carb load of a serving of cauliflower to a medium-sized baked potato, which has around 37 grams of carbohydrate. Depending on the variety of potato and its size, the possible carb count is anywhere from 22 to 45 grams—a much bigger range.

When you're trying to determine how much insulin you need, having such a wide range for potential carbs will make it more difficult to gauge, and you may be more likely to go too high or too low.

Hypoglycemic Agents

Many other medications for diabetes (particularly Type 2 diabetes) are intended to help control blood glucose. Three of the most commonly prescribed are:

• Glucophage (metformin)
• Avandia (rosiglitazone)
• Januvia (sitagliptin phosphate)

If you have been eating a higher-carb diet and switch to a low-carb one, you will likely need to change how much medication you take.

In some cases, you may be able to stop taking medication. In fact, continuing to take the same dosage could result in hypoglycemic episodes. For example, metformin, which should not cause hypoglycemia, has been known to affect some individuals with diabetes when they change their diet.

Blood Pressure Medications

High blood pressure can sometimes be partially treated with a low-carb diet. If you're already taking medication for hypertension, making changes to your diet (such as reducing your salt intake) could cause your blood pressure to go too low.

There are different types of medications used to treat hypertension. They are divided up into many drug classes, including:

• Diuretics
• Vasodilators
• Beta-blockers
• Alpha-blockers
• ACE inhibitors
• Central agonists
• Calcium channel blockers
• Alpha-2 receptor agonists
• Angiotensin II receptor blockers
• Peripheral adrenergic inhibitors
• Combined alpha and beta-blockers

Here are the brand names of the commonly prescribed blood pressure medications. While not an exhaustive list, talk to your doctor before you make changes to your diet if you're taking these or other medications to treat high blood pressure.

• Lasix
• Diuril
• Lopressor
• Toprol-XL
• Levatol
• Lotensin
• Monopril
• Diovan
• Vasocor
• Minipress
• Tenex
• Apresoline

Psychiatric Medications

Drastically reducing your carb intake, like on a keto diet, has a profound impact on your brain chemistry. In some cases, conditions like epilepsy are treated with very low-carb diets.

Specific psychiatric medications that may be affected by a low-carb diet include:

• Risperdal, Abilify, and Seroquel, and other antipsychotic drugs
• Possible increase in side effects if taking Lithium
• Anticonvulsants, including Depakote, Zonegran, and Topamax

A Word From Verywell

Everyone's unique experience with low-carb diets, medical conditions, and medication will be different. For your safety, always enlist support from your doctor, and your therapist or dietitian if necessary, before making any changes.