B12 for weight loss: does B12 help you lose weight?

Whether it’s a new diet supplement or workout trend, a new quick fix for weight loss always seems to be making headlines. Taking B12 for weight loss isn’t exactly a new idea, but it’s worth exploring if the research really backs up the marketing claims. 

So, does B12 help you lose weight? The research isn’t clear. Let’s take a look. 

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Also known as cobalamin or cyanocobalamin, Vitamin B12 is an essential nutrient that plays a role in many areas of your health. The vitamin helps produce red blood cells, DNA, and energy, and is involved in your brain, heart, and nervous system health. 

As a water-soluble vitamin, your body doesn’t store or produce B12 on its own. So, you need to get it from other sources, such as your diet or supplements. If you follow a typical Western diet, you probably have enough B12. Vitamin B12 occurs naturally in several animal products, including beef, poultry, clams, and dairy products. It’s also present in fortified foods such as cereals and nutritional yeast.

While many people can get enough B12 from their diet, not everyone does. If you’re older or follow a vegetarian or vegan diet, you may be at risk of low B12 levels. Certain autoimmune conditions and digestive issues, such as inflammation from celiac disease, can also impair your body’s absorption of vitamin B12. 

The short answer is that vitamin B12 shots probably won’t help you lose weight. B12 shots are not a scientifically proven tool for weight loss, especially for those who follow a balanced diet and get enough B12 (more on that below).

Where does the link between B12 and weight come from? Several studies have documented a link between low levels of B12 and weight gain and obesity, in both children and adults. The question is: do low B12 levels actually cause weight gain, or is it just an association and something else in people with low B12 leads to obesity? Another question in this context is, can B12 supplements help you lose weight?

According to a large sample of over 9,000 American adults, low B12 levels are associated with obesity, independent of race or ethnicity, gender, and socioeconomic and lifestyle factors. The same study also found that people with higher B12 levels are less likely to be obese. But, more research is needed to determine whether low B12 levels actually cause obesity, or if there are other contributing factors. The study also didn’t show that the vitamin can help lose weight.

In studies of mice, severely reducing their vitamin B12 levels significantly increased their body fat percentage and led to the development of fat tissue. Studies of rats have found that supplementing with B vitamins helped reduce their weight gain by improving their metabolism. However, what works for animals may not work for us, and more research regarding the effect of vitamin B12 on human body fat and metabolism is still needed.

Given B12’s role in energy and metabolism, it seems like it would make sense for B12 shots to help with weight loss. When you have enough B12, your energy levels are normal and you feel less tired. In theory, this could indirectly help with weight loss because feeling more energized makes it easier to stick to your workout routine. By the same token, feeling fatigued may make it harder to workout, which could lead to weight gain. But, no research has proven this, so it remains a theory.

More energy also translates to a faster metabolism, which means increased calorie burning and faster weight loss. And, regular exercise revs up your metabolism, so if you are working out more because you feel more energized from a vitamin B12 shot, you might enjoy a one-two punch that leads to weight loss. But, again, while this sounds logical, it hasn’t been proven out. 

What’s more, the boosts in energy and exercise performance people may enjoy from supplemental B12 don’t seem to apply if you already get enough vitamin B12 through your diet. 

Adults need 2.4 micrograms (mcg) of vitamin B12 daily, and more if pregnant or breastfeeding. If you’re looking to boost your B12 levels naturally, you’ll be happy to find that there are several foods that are high in vitamin B12. These include:

• Beef, especially beef liver

• Turkey

• Poultry

• Clams

• Tuna

• Salmon 

• Eggs

• Milk

• Yogurt 

• Cheese

• Fortified nutritional yeast

• Fortified breakfast cereal

If you ever wonder if a food contains vitamin B12, just check the nutrition label. 

You can also supplement dietary sources of B12 with over-the-counter B12. Vitamin B12 shows up in most multivitamins, and vitamin B12 supplements are available in tablet, liquid, capsule, lozenge, and even sublingual form. For vitamin B12 injections or nasal gels, you’ll need a prescription from your healthcare provider.

Low B12 levels are fairly common, with some researchers estimating that around 30% to 60% of people could have vitamin B12 deficiency. 

A severe vitamin B12 deficiency can develop into megaloblastic anemia, a condition characterized by a low red blood cell count that requires treatment. However, most people deficient in vitamin B12 only experience mild symptoms, like fatigue and pallor. (Pallor describes a paleness in your skin or appearance that derives from a specific cause. Being pale-skinned in general does not necessarily mean you are vitamin B12-deficient.)

Serious symptoms of untreated vitamin B12 deficiency may include:

• Jaundice (yellowing of the skin)

• Diarrhea

• Headaches

• Heart palpitations

• Glossitis (tongue inflammation accompanied by soreness, pain, or changes in texture or color)

• Peripheral neuropathy (nerve damage)

• Confusion

• Dementia

• Loss of balance

• Weakness 

• Changes in your sense of touch, such as tingling sensations or numbness

To diagnose a vitamin B12 deficiency, health providers usually start with a blood test. Screening for vitamin B12 deficiency is usually not recommended for the average adult. But, in cases where you have one or more risk factors, it may be recommended. 

Risk factors for vitamin B12 deficiency include:

• Following a vegetarian or vegan diet

• Being age 50 or older

• Having had gastric bypass surgery, gastrectomy, or bowel resection surgery

• Pregnancy

• Pernicious anemia

• Crohn’s disease

• Celiac disease

• Tapeworm infection

• Pancreatic insufficiency

• Bacterial overgrowth

• Zollinger-Ellison syndrome

• Inflammatory bowel disease

• Alcohol abuse 

• Damage to the small intestine

• Long-term use of medications that affect absorption of vitamin B12, including metformin, histamine blockers, and proton pump inhibitors

If your B12 levels are low, your healthcare provider may recommend oral supplements or B12 shots. Taking an oral B12 supplement can be sufficient for restoring B12 levels in vegans and older adults, while people who have more severe low B12 levels due to a health condition may need to take B12 shots.

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How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

October 17, 2023

Written by

Amelia Willson

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.