Do Dietary Supplements Cause Weight Gain?
Most dietary supplements marketed for weight loss or general health do not cause weight gain and, in fact, show little to no effect on body weight in either direction. 1, 2
Evidence on Nutritional Supplements and Weight
Weight Loss Supplements Are Ineffective, Not Weight-Promoting
The American Diabetes Association's 2024 Standards of Care provides the most definitive guidance on this topic:
There is no clear evidence that nutrition supplements (herbs, botanicals, high-dose vitamins and minerals, amino acids, enzymes, antioxidants) are effective for obesity management or weight loss. 1
Multiple large systematic reviews demonstrate that most trials evaluating nutrition supplements for weight loss are of low quality and at high risk for bias, with high-quality studies showing little or no weight loss benefits. 1, 2
These supplements are neither causing weight gain nor producing the weight loss they claim—they are essentially neutral in their effect on body weight. 1
Specific Supplement Categories
Micronutrient supplements (vitamins and minerals):
- Standard multivitamin/mineral supplements at approximately 100% of Daily Value do not cause weight gain. 3
- Vitamin/mineral supplementation (iron, vitamin B12, vitamin D) may be indicated for documented deficiencies but does not promote weight gain. 1, 2
- Calcium supplements in healthy children show no effect on weight gain (weighted mean difference +0.14 kg; 95% CI: -0.28 to +0.57 kg). 4
Protein supplements:
- May be indicated as adjuncts to medically supervised weight loss therapies, not as weight gain agents in general populations. 2
- In athletes seeking to increase muscle mass, protein supplements can support lean body mass gains when combined with resistance training, but this is context-specific. 5
Creatine:
- Can cause 1-2 kg body mass increase after loading, primarily from water retention in muscle tissue, not fat gain. 6
- This is relevant only for athletes using creatine for performance enhancement. 6
Important Caveats
Supplements That May Promote Weight Gain in Specific Contexts
In malnourished or deficient populations:
- Food supplements (not isolated nutrients) have shown positive effects on weight gain in malnourished Kenyan schoolchildren (+0.4 kg over controls). 7
- Nutritional supplements with standard polymeric formulas in HIV-infected patients resulted in 2.75% weight gain, mostly fat mass. 8
- Zinc supplementation in children recovering from severe malnutrition increased rate of weight gain. 9
These findings do not apply to generally healthy, well-nourished populations. 7, 8, 9
What Actually Causes Weight Gain
The American Heart Association emphasizes that weight gain over the past 30 years relates to:
- Increased total calorie intake (150-300 calories/day increase), with approximately 50% from liquid calories, primarily sugar-sweetened beverages. 10
- No apparent change in physical activity levels. 10
Prescription medications are a more significant concern for weight gain than supplements:
- Certain glucose-lowering medications (insulin secretagogues, thiazolidinediones, insulin) are associated with weight gain. 1
- Antidepressants (mirtazapine, amitriptyline) and antihyperglycemics (glyburide, insulin) cause weight gain. 11
- Clinicians should minimize medications for comorbid conditions associated with weight gain whenever possible. 1, 2
Clinical Bottom Line
Dietary supplements marketed to the general public do not cause clinically meaningful weight gain. 1, 2 The widespread marketing claims for both weight loss and muscle-building supplements lack scientific support, with most being ineffective rather than harmful in terms of weight. 1, 12 Focus clinical attention on actual drivers of weight gain: excess caloric intake (particularly from sugar-sweetened beverages and refined carbohydrates), sedentary lifestyle, and weight-promoting prescription medications. 10, 13, 11