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ISSA, International Sports Sciences Association, Certified Personal Trainer, ISSAonline, B12 Shots for Weight Loss: What You Need to Know

B12 Shots for Weight Loss: What You Need to Know

Reading Time: 5 minutes 20 seconds


DATE: 2022-05-16

When your goal is weight loss, it can feel like an uphill battle. You know the importance of healthy food. Yet, you’re tempted by high-fat, high-calorie options. You understand that your physical activity should increase, but it’s hard to find the time or a high enough energy level.

Some claim that vitamin B12 shots are the answer to weight loss. Here we explore how this vitamin can impact weight. We go into what science says about the effectiveness of a B12 shot. We also compare a b12 injection with a lipotropic injection, so you know the difference. 

Who should get a shot and who should avoid it? We’ll cover that too. Next, we go into how to increase this B vitamin through diet versus injection. For trainers, we also share how you can provide clients with the best nutritional advice related to vitamin B12 and weight loss.

What is Vitamin B12?

Vitamin B12 is required for creating new red blood cells. It is necessary for the healthy functioning of nerves and the brain. Vitamin B12 is cobalamin an enzyme co-factor that is necessary for the synthesis of DNA. B12 is also involved in the synthesis of hormones and neurotransmitters.

B12 is mainly found in meat, poultry, fish and shellfish, eggs, and dairy. Non-animal sources include fortified or enriched milk substitutes, grains, and nutritional yeast.

So, is weight loss with shots of B12 plausible?

B12 and Weight Loss: How a B12 Shot Can Support Weight Loss

Vitamin B, in general, increases energy. Two B vitamins are credited with providing the greatest energy benefits. They are vitamin B6 and vitamin B12.

Vitamin B6 is also known as pyridoxine. It helps regulate glycogen, which impacts energy levels. It also affects appetite. Vitamin B12 is also known as cobalamin. It plays a role in cell metabolism. This impacts whether you feel energy or fatigue.

In fact, increased energy is one of the most promised benefits of B12. This enhanced energy makes it easier to get to the gym. You can also work out harder because you don’t feel fatigued. But do B12 injections actually promote weight loss? 

Effectiveness of Vitamin B12 for Losing Weight

Most of the vitamin B12 weight loss research involves people who’ve had weight loss surgery. In these cases, the B12 supplement shots were to help correct or protect against B12 deficiency. Others have assessed B12 shots for reducing deficiency due to other causes. 

No studies could be found that assess a B12 injection’s impact on weight loss efforts in humans. (There are several studies involving animals, but not human subjects.) What research does show is that people who are overweight tend to be low in vitamin B12. 

One such piece of research is a 2020 review published in the journal Nutrients (1). In it, researchers connected vitamin B12 deficiency and increased body weight. This connection existed in both children and adults. It also noted that as B12 deficiency increased, so too did insulin resistance. Thus, low vitamin B12 levels may contribute to obesity.

A 2014 study involving 976 subjects reported similar results (2). Those with low vitamin D levels were overweight more often than people with higher vitamin levels. Their body mass index was higher as well. 

Vitamin D levels were also lower in people with metabolic syndrome. This syndrome involves having a variety of health issues at the same time. Among them are high blood pressure, high cholesterol, and high blood sugar. This increases one’s risk of major medical conditions such as heart disease and type 2 diabetes.

In the end, research makes a connection between low vitamin B12 and increased weight. But it is still unclear whether B12 injections can promote weight loss in humans. 

Vitamin B12 Injections vs Lipotropic Injections

There are different types of weight loss injection. So, vitamin B12 shots are sometimes confused with lipotropic injections. 

Lipotropic injections do typically contain vitamin B12. But they contain other nutrients as well. Depending on the injection, it might include other B vitamins. It might also contain branched-chain amino acids and L-carnitine. Some lipotropic B12 injections contain phentermine. Phentermine is an amphetamine-like drug that helps decrease hunger. 

This is important because higher doses of vitamin B12 aren’t generally a problem. The same isn’t always true for ingredients found in lipotropic injections.

The National Library of Medicine shares that phentermine can raise blood pressure (3). It may even affect insulin levels. This can create an issue for people with diabetes. It’s also not recommended for older adults.

Who Might Benefit from Vitamin B12 Injections

At this time, it is unknown whether a B12 injection can assist with a weight loss program. Who might these shots be good for then?

If a client has a vitamin B12 deficiency, they might benefit from an injection. Megaloblastic anemia is one such deficiency, a macrocytic anemia that causes bone marrow to create very large red blood cells. Most people do get enough of this vitamin in their diet. Yet, a deficiency exists in as many as 43% of older adults (4). 

A deficiency in this vitamin can create a variety of symptoms. Among them are fatigue, dizziness, and muscle weakness. It can also result in confusion and personality changes. 

The Mayo Clinic shares that those most at risk of low levels include (5):

  • people who don’t consume enough vitamin B12 in their diet

  • people diagnosed with pernicious anemia

  • people who’ve had gastric surgeries

  • people with intestinal issues, such as celiac or Crohn’s disease

People following a vegetarian diet are especially at risk of deficiency. This is because vitamin B12 is primarily in animal-based foods. Research suggests that this is even more important for women who are pregnant or lactating (6). This helps ensure that the developing baby gets enough of this important vitamin.

If clients have concerns about their B12 level, their doctor can do a blood test. These results can provide insight into whether a B12 deficiency exists. Clients should always consult with their doctors before trying new supplements or changes to their diet.

When B12 Shots for Weight Loss Are Not Recommended

Vitamin B12 injections aren’t for everyone. In some cases, a vitamin B12 shot can interfere with other medications. This can cause those medications to be ineffective. 

The University of Michigan also warns that a B12 shot is not recommended for people with Leber’s disease (7). This is a disease that causes a loss of vision. It also suggests talking to your doctor first if you:

  • have kidney or liver disease

  • have any type of infection

  • are receiving treatment that affects bone marrow

Encourage clients to talk with their doctor before trying to achieve weight loss with vitamin B12 injections. This helps prevent these types of issues.

Vitamin B12 Injection Safety

If a client decides that they want to try B12 shots for weight loss, that’s up to them. Following a few general guidelines can help them stay safe.

First, they should get the shots from a reputable provider. One option is from their doctor. If they use the services of a medical weight loss clinic, it might also offer vitamin B12 injections for weight loss. 

What about dosage? Older research indicates that 1,000 micrograms per injection helps reduce vitamin B12 deficiency (8). It also suggests getting five or six injections bi-weekly to “load” the body. This should be followed by once-monthly B12 injections. This helps maintain healthier B12 levels.

The Mayo Clinic adds that some people experience side effects with a vitamin injection (9). These effects can include: 

  • abdominal pain

  • chest pain

  • cough

  • dizziness

  • eye pain

  • irregular heartbeat

  • ringing in the ears

  • weight gain 

While some of these effects are merely uncomfortable, others are cause for concern. If a client has side effects after a B12 injection, they should talk to their doctor. This helps them decide whether this option is safe for them.

How to Increase Vitamin B12 Without an Injection

Clients can increase their vitamin B12 level without an injection. They do this by adding certain foods to their diet. Foods that are rich in vitamin B12 include:

  • Fish (salmon, trout, tuna, and sardines)

  • Shellfish (clams)

  • Organ meat (liver and kidneys)

  • Beef

  • Milk

  • Yogurt

  • Cheese

  • Eggs

  • Fortified cereal

A balanced meal plan can provide the nutrients clients need to support a healthy weight loss journey. It can also reduce the risk of weight gain due to unhealthy food choices.

Learn how to create customized meal plans by becoming a certified nutritionist. ISSA’s Nutritionist Specialization Certification course teaches trainers how to determine a client’s dietary needs, whether they want to lose weight or gain muscle. This information can be used to create an eating plan that meets those needs. You also learn which strategies work best for promoting successful lifestyle changes.

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ISSA | Nutritionist

By becoming an ISSA Nutritionist, you'll learn the foundations of how food fuels the body, plus step by step methods for implementing a healthy eating plan into clients' lifestyles.


  1. Boachie, J., Adaikalakoteswari, A., Samavat, J., & Saravanan, P. (2020). Low Vitamin B12 and Lipid Metabolism: Evidence from Pre-Clinical and Clinical Studies. Nutrients, 12(7), 1925. https://doi.org/10.3390/nu12071925

  2. Baltaci, D., Kutlucan, A., Turker, Y., Yilmaz, A., Karacam, S., & Deler, H. et al. (2013). Association of vitamin B12 with obesity, overweight, insulin resistance and metabolic syndrome, and body fat composition; primary care-based study. MEDICINSKI GLASNIK, 10(2), 203-210. Retrieved 22 April 2022, from https://ljkzedo.ba/sites/default/files/Glasnik/10-02-aug2013/mg_cijeli.pdf#page=11.

  3. Drugs, H. (2017). Phentermine: MedlinePlus Drug Information. Medlineplus.gov. Retrieved 22 April 2022, from https://medlineplus.gov/druginfo/meds/a682187.html.

  4. Vitamin B12. Ods.od.nih.gov. (2021). Retrieved 22 April 2022, from https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/.

  5. Vitamin deficiency anemia - Symptoms and causes. Mayo Clinic. (2022). Retrieved 22 April 2022, from https://www.mayoclinic.org/diseases-conditions/vitamin-deficiency-anemia/symptoms-causes/syc-20355025.

  6. Zeuschner, C.L., Hokin, B.D., Marsh, K.A., Saunders, A.V., Reid, M.A. and Ramsay, M.R. (2013), Vitamin B12 and vegetarian diets. Medical Journal of Australia, 199: S27-S32. https://doi.org/10.5694/mja11.11509

  7. Cyanocobalamin (injection) | Michigan Medicine. Uofmhealth.org. (2019). Retrieved 22 April 2022, from https://www.uofmhealth.org/health-library/d00413v1.

  8. Watts D. T. (1994). Vitamin B12 replacement therapy: how much is enough?. Wisconsin medical journal, 93(5), 203–205.

  9. Cyanocobalamin (Intramuscular Route) Side Effects. Mayo Clinic. Mayoclinic.org. (2022). Retrieved 22 April 2022, from https://www.mayoclinic.org/drugs-supplements/cyanocobalamin-intramuscular-route/side-effects/drg-20137833?p=1.

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