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  • Kelin M

B12 for Weight Loss: Does it Work?

If you've had trouble losing weight, you may have heard that taking extra B-12 could help you shed those extra pounds. But is it true?

The answer is: it depends. B-12 (also known as cobalamin), like other B vitamins, converts the food we consume into energy and there's evidence that your B vitamin consumption affects your metabolism.

B12 supplementation is only useful if you already have a deficiency, so first let's understand what B12 is, signs you could be low, and who's at highest risk for B12 deficiency.

We'll then go over what current research says about how consuming more B12 could help you meet your weight loss goals and the impact it could have on your metabolism.

What is B-12?

This critical water-soluble vitamin is responsible for healthy blood and nerve cell function, making DNA, and preventing pernicious anemia (which can make you feel weak and tired).

It's found primarily in animal products. The best sources of B12 are:

  • Meat, especially organ meats (liver and kidney)

  • Small fish (sardines, clams, and tuna)

  • Large fish (tuna, salmon, and trout)

  • Milk and dairy products (yogurt and cheese)

  • Eggs

  • Fortified cereals, bread, nutritional yeast

In addition to natural sources, supplements (like the Why Not Natural B12) are very effective at improving B12 levels.

Signs You're Low in Vitamin B12

Are you feeling too exhausted to keep up with an exercise routine? Grabbing convenient foods because you're too tired to prepare anything else? Exhaustion is a sign of B-12 deficiency.

Here are some other signs that indicate low vitamin B12 to keep an eye out for:

  • Pale skin or jaundice

  • Pins and needles in hands and feet

  • Problems with balance and coordination

  • Swollen, inflamed tongue

  • Shortness of breath

  • Spells of dizziness

  • Mood changes or dementia

  • Changes to vision

These symptoms don't necessarily indicate low B-12 on their own, but if you're experiencing one or more of the above you may be deficient. Consult with your doctor for a blood test if you're worried!

Who is at Highest Risk for Low B-12?

Ironically, some of the healthiest people are the most likely to be low in vitamin B-12.

Those on a Plant-Based Diet

The primary risk factor for low B-12 is a vegetarian or vegan diet. Since many of the foods that are rich in B-12 are animal products, plant-based diets tend to be low unless they contain a lot of processed, fortified foods.

One of the best options for vegetarians and vegans is to take a natural sublingual supplement each day. Deficiencies can take years to show up in blood results, so it's safer to be proactive.

Bariatric Surgery Patients

Another high-risk group is those who have had bariatric or weight-loss surgery (banding or sleeve). Individuals in this group have improved health outcomes overall, but the effect on their B12 levels without supplementation can be catastrophic.

People over 60

People over 60 are at especially high risk of B-12 deficiency as well. As many as 10-15% of people in this group are thought to have a deficiency, because of the changing conditions of their stomach and intestine which affects absorption.

Pregnant Women

Pregnant women have higher B12 needs than the rest of the population (2.6 mcg per day). Consuming enough during pregnancy is especially important for the infant, as those born to mothers who are deficient may have birth defects. They're also at higher risk of being born prematurely and having low birth weight.

Breastfeeding Women

Breastfeeding women have even higher B12 needs (2.8 mcg per day). Low B12 in breastmilk can impair proper brain development of the breastfeeding child.

Infants with low B12 levels are also more irritable, have lower appetites, and can even experience failure to thrive.


Certain factors like consuming a plant-based diet, being over 60, having surgery that removes part of the intestine, or being pregnant/lactating can increase your B12 needs or make you more likely to have low levels.

Being in a high-risk group makes you more likely to have a deficiency but anyone can experience low B12 due to undiagnosed problems like low intrinsic factor (a protein that aids in absorption of B12). When in doubt, see a healthcare professional!

How B-12 Supplementation Can Help You Lose Weight

B-12 supplementation alone won't make you lose weight. It's only effective if you're already low in B-12.

While many centers offering B-12 injections claim it's an effective weight loss supplement, there aren't a lot of studies to back this up. B-12 on its own may not have a dramatic effect on your body composition, but deficiency in one B vitamin can affect the levels of others, which can negatively impact your metabolism.

A 2018 study showed that rats on a high-fat diet who were given a range of B vitamins had increased metabolisms and reduced body weight gain! B-12 specifically is necessary for metabolism of fat and protein.

As more studies are performed on humans, we will further understand the role that B vitamins play on metabolism and weight gain.

Another important note: if you're gaining weight because you're too exhausted to get adequate exercise, low B-12 could be the reason.

If you're low in B-12 and it's causing you to feel depressed, it can be hard to stay motivated to eat properly and exercise. It might be worth supplementing for a few weeks to see if it makes a difference, as B12 is a very safe supplement.

How Much B-12 for Weight Loss

If you or your doctor have determined you have low B-12, he or she may prescribe injections. You can also take B12 orally to reverse a deficiency!

The recommended daily allowance (RDA) is 2.4 mcg for those over 14 years of age. However, this quantity won't work for everyone.

Your body only absorbs a small amount of what you consume in a supplement.

Cobalamin (or B12) binds with intrinsic factor to be absorbed. Under 1 or 2 mcg, about 50% can be bound and absorbed. Above this amount, however, the binding capacity of the intrinsic factor is exceeded, and your body only absorbs a very small percentage of what you consume.

In other words, you'll need to take far more than you think to reverse a deficiency using supplements. It's estimated that you'll only absorb 10 mcg of a 500 mcg dose.


B12 on its own won't make you lose weight if you already consume enough. However, if you're low in B12, it could make a difference in helping you reach your weight-loss goals!

Some groups (like those over 60 or vegetarians) are particularly likely to have a B12 deficiency.

If you do have a B12 deficiency, you may need to supplement with more than the recommended daily value of 2.4 mcg. The amount you absorb is depended on the amount of intrinsic factor available.

Supplementing with B12 and reversing your deficiency will leave you feeling more energized, in a better mood, and may heal problems with your metabolism. B vitamins work together as a critical part of a healthy, functioning metabolism.

You should always consult with your doctor if you suspect a deficiency or are experiencing sudden weight gain or other metabolic problems.

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