7 foods to avoid while taking metformin

Metformin is an FDA-approved drug for the treatment of Type 2 diabetes. It has a long history of success in lowering blood sugar levels, especially when combined with diet changes and exercise. Although metformin is only approved for use in treating Type 2 diabetes, it has several off-label uses, including as a treatment for polycystic ovary syndrome (PCOS), gestational diabetes, and drug-induced weight gain.

Most people can safely take metformin. It’s generally well-tolerated—but it can cause digestive side effects, like vomiting and diarrhea. You can limit these side effects (and improve metformin’s overall effectiveness) by eating the right combination of foods each day. This means avoiding foods that increase your blood sugar, like those high in sugar, sodium, and saturated fats. Here are seven foods and drinks to avoid while taking metformin and what you can eat to help lower your blood sugar even further.

How metformin works

Metformin is part of a class of drugs called biguanides and is used to treat Type 2 diabetes. It improves your blood sugar levels by doing two things: decreasing the amount of glucose released into your bloodstream and increasing your body’s insulin sensitivity.

Lower blood sugar levels lead to better overall health for people with diabetes; having Type 2 diabetes and high blood sugar increases your risk for heart disease, stroke, and organ failure.

Metformin is a commonly prescribed medication to lower blood sugar, and according to Danielle Kelvas, MD, a primary care physician with The HCG Institute in Tennessee and founder of DKMD Consulting, it works fairly quickly: many people start to see benefits after just one month, with more noticeable improvements to blood sugar and A1C levels after three months.

7 foods to avoid with metformin

Technically, there are no foods that directly interact with biguanides like metformin, but there are still some you should try to avoid or limit. Why? Because they encourage weight gain and directly counteract the positive effects metformin has on your blood sugar levels, says Dr. Kelvas.

The good news is that many of your daily favorites—like coffee, fruit, whole grains, and eggs—are fine to continue eating and drinking as part of a balanced diet with metformin. The vitamins and supplements you take are likely safe, too. Most of the foods you should avoid while taking metformin fall into the following categories:

1. Simple/refined carbs
2. High sugar foods
3. High sodium foods
4. Saturated fats
5. Alcohol
6. Excessive fiber
7. Processed foods

The outlier in this list is alcohol; it’s the one thing that makes metformin less effective because both alcohol and metformin are metabolized in the liver. (The recommendations to avoid the other foods on this list exist because these specific foods can cancel out many of metformin’s benefits, not because they specifically interact with the drug).

1. Simple and refined carbs

Simple and refined carbohydrates like white bread, pasta, white rice, muffins, and sweetened beverages can cause rapid spikes in blood sugar, says New Jersey-based dietitian Erin Palinski-Wade, RD, CDCES, author of 2 Day Diabetes Diet, which can make metformin less effective at controlling blood sugar levels.

Instead of simple carbs, Palinski-Wade suggests choosing foods with complex carbohydrates (think whole grain foods like oatmeal, brown rice, and wheat bread) and combining them with proteins and healthy fats to help improve blood glucose regulation while taking metformin.

2. High sugar foods

Similarly, foods high in added sugar can increase insulin resistance, says Palinski-Wade, rendering metformin less effective for people taking the drug to lower their blood sugar levels. Try to stay under the recommended daily limit for added sugar, which is six teaspoons for women and nine teaspoons for men.

This seems easy to do, but added sugar is hiding in many of our foods and drinks. Even healthy foods like yogurt can have extra-high amounts of added sugar, as can condiments like salad dressing and ketchup. Also, keep an eye on your favorite beverages. While Dr. Kelvas says it’s fine to drink regular coffee when taking metformin, she cautions against drinking really sugary coffee drinks (like flavored lattes and frappuccinos). Stick to plain black coffee with a splash of your milk of choice.

It’s also important to note that added sugar is not the same as natural sugar. It’s okay to eat fruits and vegetables with a higher sugar content in moderation (i.e., bananas and sweet potatoes) because natural sugars don’t affect your blood sugar levels the same way as added sugars do.

3. High sodium foods

Foods that are high in sodium, like frozen dinners, smoked meats, processed cheeses, and canned vegetables, can lead to an increased risk of hypertension, says Palinski-Wade, and this poses a problem for people taking metformin, who are typically already insulin-resistant and at a higher risk of heart disease.

“The recommended daily sodium intake is generally 2,300 milligrams per day for healthy adults,” she explains, “but for certain individuals, such as those with high blood pressure, diabetes, or kidney disease, the recommended limit is 1,500 milligrams per day.”

You don’t have to cut out all sodium, but when taking metformin, it’s a good idea to focus on eating a low-sodium diet by cooking more often at home, reducing salt in your meals, and making low-sodium food substitutions (like swapping processed cheese slices for fresh mozzarella).

4. Saturated fats

Palinski-Wade says saturated fats can increase inflammation and worsen insulin resistance, which can counteract the effects of metformin. Common sources of saturated fat include red meat, butter, cheese, and other full-fat dairy products like ice cream, as well as fried foods, coconut oil, and baked goods.

Before you start worrying about giving up some of your favorite foods, know this: Palinski-Wade says you don’t have to avoid saturated fats completely but should try to limit them to 10% or less of your total daily calories.

5. Alcohol

Metformin and alcohol are both metabolized in the liver, so Dr. Kelvas says it’s important to restrict your alcohol consumption to no more than one to two drinks per day; excessively drinking alcohol will stress your liver, directly raise your blood sugar levels, and reduce metformin’s efficacy in lowering your blood sugar levels.

Drinking too much alcohol on a regular basis while taking metformin could also cause serious complications like lactic acidosis, says Yoshua Quinones, MD, an internist with Medical Offices of Manhattan, a condition that occurs when too much lactic acid builds up in your bloodstream.

6. Excessive fiber

Although fiber is usually good for people with diabetes, Dr. Quinones says eating a lot of fiber-rich foods all at once might affect how metformin is absorbed, possibly reducing its ability to control blood sugar levels effectively.

“It’s better to eat fiber steadily throughout the day and drink enough water,” he adds. “While it’s unnecessary to avoid high-fiber foods completely, you should be cautious about consuming excessive amounts in one meal.” Specifically, eating large amounts of fiber at the same time as your metformin. Some foods with a high-fiber content include leafy greens, legumes, apples, kiwis, bran cereals, brown rice, and popcorn.

7. Processed foods

According to Palinski-Wade, processed foods are foods that have been changed from their natural state in some way; this can include everything from milling, cutting, and heating foods to pasteurizing, cooking, canning, and freezing them.

In other words, not all processed foods are bad—baby carrots are a processed food, Palinski-Wade notes. However, so are candy bars, so it’s important to look at a food’s nutrition label and understand how certain types of preparations can affect the overall nutritional value.

“Ultra-processed foods with large amounts of added sugar, sodium, and/or saturated fat can have a negative impact on health when consumed as the majority of your diet,” says Palinski-Wade. As we’ve pointed out, foods high in sugar, sodium, and saturated fat can interfere with metformin’s ability to lower your blood sugar and help keep your weight within a healthy range.

Herbs and supplements to avoid with metformin 

According to Dr. Quinones, most vitamins are safe to take with metformin. In fact, you may want to add vitamin B12 to your diet, he says, because extended use of metformin may lower vitamin B12 levels and cause symptoms like fatigue and numbness. If you’re on long-term metformin therapy, Dr. Quinones recommends talking to your healthcare provider about monitoring your B12 levels.

However, there is one supplement that you may want to avoid: ginseng. “Combining metformin with ginseng could potentially amplify its effects on blood sugar levels,” Dr. Quinones says. “It may be necessary to monitor your blood sugar more frequently when using both medications together to ensure safe usage.”

What should you eat while taking metformin?

According to Dr. Kelvas, foods to eat while taking metformin include any foods that help lower your blood sugar: lean protein, fresh, non-starchy vegetables, and healthy fats like avocados, nuts and nut butter, olive oil, and fish. You can also include plenty of whole grain bread, seeds, and fruits like berries in your diet to naturally reduce your blood sugar.

You may also want to ask your provider about switching to the extended-release tablet of metformin; Dr. Kelvas says this formulation may be better for your digestion and absorption of metformin than the immediate-release formulation, partly because the extended-release formulation tends to cause less nausea and diarrhea.

Gastrointestinal side effects of metformin

While metformin can help people with diabetes lower their blood glucose levels, it may also cause digestive symptoms or change bowel habits. According to Dr. Kelvas, the more common side effects are diarrhea and nausea, which can definitely be exacerbated by continuing to eat the foods to avoid being included on this list.

Dr. Quinones also suggests taking metformin with meals, especially when you’re just beginning treatment, staying hydrated, starting with a lower dose, and then slowly increasing the amount of metformin you take over time.

However, there are a few GI symptoms that should prompt you to get medical advice; if you’re on metformin and having extreme nausea or vomiting, stomach pain, or decreased appetite, contact a healthcare professional right away or seek emergency medical attention.