Kat Barefield, MS, RD, CPT

One of the key functions of B vitamins is extracting energy from food to either be used immediately by cells to fuel various metabolic reactions or stored for later use. Because of this, some are concerned that consuming extra B vitamins can lead to unwanted weight gain.

This article will answer that question and cover a bit more, including:

  • The key functions of B vitamins
  • Why B vitamins are added to the food supply
  • Which vitamins you may be lacking
  • The evidence on whether consuming excess B vitamins leads to weight gain
  • Keep reading to get the full scoop.
B Vitamin

Chief Function of B Vitamins

The B vitamins include:

  • Thiamine – B1
  • Riboflavin – B2
  • Niacin – B3
  • Pantothenic acid – B5
  • Pyridoxine – B6
  • Biotin – B7
  • Folate/folic acid – B9
  • Cobalamin – B12

Choline is not a vitamin since the body produces minimal amounts, but it is an essential micronutrient similar to the B vitamins. Therefore, choline is included in this group.

B vitamins are one of the six types of nutrients that are essential for the proper functioning of the trillions of cells which make up the human body. By definition, “essential nutrient” means it’s something required to sustain life, but the body doesn’t make it so we must consume it on a regular basis. B vitamins are water soluble and excess amounts are excreted in urine, sometimes resulting in a harmless bright yellow color.

Some of their functions include:

  • Converting protein, carbs and fat into energy cells can use
  • Breaking down glycogen and producing glucose
  •  Synthesizing other compounds such as cholesterol, fatty acids and neurotransmitters which help regulate appetite
  • DNA synthesis and replication
  • Helping to maintain proper function of the nervous system
  • Producing and assisting antioxidants

Good Sources of B Vitamins

B vitamins can be found in many different foods as shown in the table below.

Foods/Food Group

B Vitamins

Fortified grains – cereals, breads, pastas

B1, B2, B3, B5, B6, B7, Folic acid, B12

Legumes – beans, peas and lentils

B1, B5, Folate

Fruits and vegetables

B1, B2, B3, B5, B6, B7, Folate, Choline

Meat, fish, poultry

B1, B2, B3, B5, B7, B12, Folate

Organ meat

B2, B5, B6, B7, Choline

Milk and milk products

B1, B2, B3, B5, B6, B7, B12


B2, B5, B7, B12, Choline, Folate

Nuts and seeds

B1, B2, B3, B5, B6, B7, Folate


Consuming a wide variety of foods from all the major food groups helps prevent deficiency, which is a rare occurrence in most developed countries. One reason for this is the addition of B vitamins to grain products such as breads, cereals and pasta. In the early 1940’s, wheat flour was enriched with thiamin, riboflavin, niacin and iron and infant formulas were fortified with vitamins. In 1998, grains were fortified with folic acid in the United States.

Vitamin Intakes in the US

Daily amounts of each of the B vitamins that you should aim to consume are known as the Recommended Dietary Allowance (RDA). The RDAs are based on gender, age, and life stage such as pregnancy and lactation. Most Americans consume enough of most of the B vitamins, but still fall short of others.

Although vitamin deficiencies are rare, data from over 15,000 Americans at least 9 years of age shows that nearly one third of the U.S. population is at risk of deficiency for at least one vitamin and anemia (lack of iron). [1]

Higher risks of deficiency were observed in certain people:

  • Women
  • Blacks
  • Low-income households
  • Underweight
  • Obese

The highest risk of deficiency was among non-users of dietary supplements compared to those who used a full-spectrum multivitamin and mineral and other dietary supplements.

Although not deficient, even more individuals fall significantly short of daily recommended amounts of several vitamins and minerals, as highlighted by the 2020 Dietary Guidelines for Americans Report, written by a committee of 20 nutrient scientists, physicians and dietitians from various hospitals and universities across the country. [2]

Nutrients Americans are Falling Significantly Short Of

Vitamin A


Iron (females of reproductive age)

Vitamin C



Folate (females of reproductive age)

Vitamin D



Protein (adolescents and older adults)

Vitamin E


Vitamin B12 (older adults)

Vitamin K

Dietary Fiber



Here are some of the reasons you and many others may not be getting enough of certain micronutrients:

  • Following a popular diet that severely restricts or eliminates specific foods or food groups
  • Avoiding various food groups such as carbs, dairy, meat and gluten due to preferences, allergies or intolerances
  • Eating the same foods with little variety
  • Cutting calories to lose weight
  • Alcoholism, gastrointestinal disease, and eating disorders
  • Additionally, choline has been identified by nutrition scientists as a nutrient of concern, especially during pregnancy and breastfeeding. Most Americans don’t get enough, and it’s needed as part of the structure of every cell in the body. 2

To learn what can happen if you’re not getting recommended amounts of vitamins and minerals, check out this article .

B Vitamins and Weight Gain

It’s been hypothesized that excess B vitamin intake coupled with high carbohydrate intake lead to converting more carbs into fat storage, thus resulting in weight gain. And because many people consume the majority of their calories from carbohydrates, the combination of B vitamins in our food supply and supplements has been implicated as a potential contributing factor in the obesity epidemic.

Two published papers present observational data associating the sharp rise in obesity with the fortification of foods with B vitamins. [3] , [4] However, with all observational research, a correlation between two variables does not mean one caused the other or vice versa.

The old adage goes “correlation does not equal causation.” This is a critical point when interpreting research and is often missed by media outlets which deliver headlines to make the news. Consider the following:

Other occurrences that paralleled food fortification and the rise in obesity include technological advancements, less time spent outdoors, increased availability of food, more hyperpalatable processed snack foods, more screen time, reduced physical education in schools, and higher calorie intakes.

In order to determine whether excess B vitamins cause weight gain and hence the rise of obesity, a randomized clinical trial would have to be conducted in humans with two groups consuming the appropriate number of calories to maintain their body weight. One group would be given a placebo, and the other would be given extra B vitamins. At present, there is no such research.

Vitamins and Weight Management

There is research that suggests that the use of multivitamins may be helpful for weight management. One study was observational in nature and looked at the use of a multivitamin and mineral supplement and body composition and the other was a clinical trial in humans. [5]

In the observational study, nearly 600 men and women were studied and those who took multivitamins had lower fat mass and body weight compared to those who didn’t take supplements. Interestingly, women who took supplements reported feeling less hungry compared to non-users.

In the clinical trial, 45 obese individuals were randomly assigned to one of two groups: 1) multivitamin and mineral or 2) placebo. Both groups were asked to reduce their daily intake by 700 calories for 15 weeks. Here are the results:

  • Both groups lost weight, with no significant differences between the groups
  • There were no significant differences between the groups in energy expenditure
  • Women taking the multivitamin supplements reported lower ratings in appetite

The researcher concluded the following:

“Overall, this suggests that an appetite-modulating effect of vitamin and mineral supplements could be more significant in individuals characterized by inadequate intake in micronutrients.”

Based on the data so far, it’s impossible to conclude that excess B vitamins cause weight gain. It’s more plausible that adequate vitamin intake may be helpful for appetite, particularly in women. As noted, restricting calories for weight loss not only worsens micronutrient inadequacies but also increases appetite.


The way we gain weight is by consuming calories above what the body uses. Although vitamins and minerals are needed to extract energy from the food we eat, B vitamins alone won’t result in weight gain. In fact, most people are falling short of the various vitamins and minerals we need to support overall health, metabolism and longevity.

Therefore, to prevent unwanted weight gain, consume a wide variety of nutrient rich foods, and keep your calorie intake in balance with your daily output.

By taking a complete multivitamin and mineral for your age, gender, life stage and activity level, you raise the likelihood of getting all the essential nutrients needed for optimal functioning of your metabolism.

Lastly, don’t use a multivitamin and other supplements as an excuse to skip out on leafy greens, bright fruits and veggies and other nutrient dense foods. Rather, use a full spectrum multivitamin to fill the gaps and complement your food choices and avoid mega-dosing on vitamins unless a licensed professional advises you to do so.

Do you want to see which multivitamin is right for you? Take our supplement screener questionnaire to find out.


[1] Bird JK, Murphy RA, Ciappio ED, McBurney MI. Risk of Deficiency in Multiple Concurrent Micronutrients in Children and Adults in the United States. Nutrients. 2017 Jun 24;9(7):655. doi : 10.3390/nu9070655. PMID: 28672791; PMCID: PMC5537775.

[2] Dietary Guidelines Advisory Committee. 2020. Scientific Report of the 2020 Dietary Guidelines Advisory Committee: Advisory Report to the Secretary of Agriculture and the Secretary of Health and Human Services . U.S. Department of Agriculture, Agricultural Research Service, Washington, DC.

[3] Zhou SS, Zhou Y. Excess vitamin intake: An unrecognized risk factor for obesity. World J Diabetes . 2014;5(1):1-13. doi:10.4239/wjd.v5.i1.1

[4] Taleban R, Heidari -Beni M, Qorbani M, et al. Is dietary vitamin B intake associated with weight disorders in children and adolescents? The weight disorders survey of the CASPIAN-IV Study. Health Promot Perspect . 2019;9(4):299-306. Published 2019 Oct 24. doi:10.15171/hpp.2019.41

[5] Major GC, Doucet E, Jacqmain M, St-Onge M, Bouchard C, Tremblay A. Multivitamin and dietary supplements, body weight and appetite: results from a cross-sectional and a randomised double-blind placebo-controlled study. Br J Nutr . 2008 May;99(5):1157-67. doi : 10.1017/S0007114507853335. Epub 2007 Nov 1. PMID: 17977472.

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