Beyond the Scale: How Nutrient Deficiencies Affect Weight Loss

By Rohan Smith | Functional Medicine Practitioner — Adelaide, South Australia

Quick Answer

For some people, weight loss remains difficult despite consistent dieting and exercise. In these cases, underlying nutrient deficiencies may be contributing to weight loss resistance. Nutrients such as vitamin D, magnesium, iodine, and iron play important roles in metabolism, energy production, and hormonal regulation. When these nutrients are insufficient, metabolic efficiency can be impaired, making fat loss more challenging. Understanding and addressing these deficiencies may help explain stalled progress and support more sustainable weight loss outcomes (1–4).

Why Nutrient Deficiencies Matter in Weight Loss

Efficient metabolism relies on adequate nutrient availability. When key nutrients are lacking, metabolic pathways involved in energy production, hormone signalling, and fat utilisation may function less effectively. Nutrient deficiencies can also influence appetite regulation, insulin sensitivity, stress physiology, and fat storage, creating conditions that make weight loss more difficult even when lifestyle efforts are appropriate (5–7).

Key Nutrients for Weight Loss

Several nutrients are particularly important for metabolic health and weight regulation:

Vitamin D

Vitamin D plays a role in insulin sensitivity, inflammatory signalling, and adipose (fat) tissue metabolism. Low vitamin D status has been associated with increased fat mass, impaired fat oxidation, and reduced metabolic efficiency. Adequate vitamin D levels may support healthier glucose handling and energy balance (1,8). Dietary sources include fatty fish, egg yolks, and fortified foods, while sunlight exposure contributes significantly to vitamin D production.

Magnesium

Magnesium is required for hundreds of enzymatic reactions, including those involved in glucose metabolism, ATP production, and stress regulation. Insufficient magnesium intake has been associated with insulin resistance, fatigue, heightened stress responses, and reduced exercise tolerance, all of which may interfere with weight loss efforts (2,9,10). Common dietary sources include leafy greens, nuts, seeds, and whole grains.

Iodine

Iodine is essential for the synthesis of thyroid hormones, which regulate basal metabolic rate, energy expenditure, and fat oxidation. Inadequate iodine intake may impair thyroid hormone production, potentially leading to a slower metabolism and increased difficulty losing weight. This relationship is explored further in the context of
thyroid function and metabolic health (3,11,12).
Iodine-rich foods include seafood, seaweed, and iodised salt.

Iron

Iron supports oxygen transport, mitochondrial energy production, and physical performance. Low iron status can result in fatigue, reduced exercise capacity, and impaired aerobic metabolism, which may indirectly hinder weight loss by limiting activity levels (4,13,14). These patterns are commonly observed in individuals experiencing
chronic fatigue and low energy states.
Iron is found in foods such as lean meats, legumes, and leafy green vegetables.

How to Identify Nutrient Deficiencies

When weight loss remains difficult despite appropriate diet and exercise, nutrient insufficiencies may be worth investigating. Pathology testing can help assess levels of nutrients such as vitamin D and iron, along with markers related to iodine and magnesium status. In some cases, broader biochemical testing, such as a
methylation panel,
may provide additional insight into how nutrient status and metabolic pathways are interacting. Interpreting results in context is important, as patterns across multiple markers often provide more clinically useful information than a single value in isolation (15,16).

Addressing Nutrient Deficiencies for Weight Loss Support

Once deficiencies or insufficiencies are identified, targeted strategies may help restore balance:

• Vitamin D: Increasing safe sun exposure or supplementing when clinically indicated.
• Magnesium: Emphasising magnesium-rich foods or using supplemental forms when appropriate.
• Iodine: Including iodine-containing foods such as seafood or iodised salt.
• Iron: Adjusting dietary intake or supplementing when deficiency has been confirmed.

How Nutritional and Functional Medicine Can Help

A functional medicine approach considers how nutrition, lifestyle, and underlying biochemical patterns interact to influence metabolic health. Rather than focusing solely on calorie intake, this approach aims to identify contributing factors such as nutrient insufficiencies, hormonal influences, and metabolic stressors that may drive weight loss resistance. Personalised testing and targeted nutritional strategies are used to support overall metabolic function.

How I Can Support You

As a functional medicine practitioner with over a decade of clinical experience, I work with individuals to identify potential nutrient imbalances and develop personalised strategies to support metabolic health. By addressing contributing factors rather than symptoms alone, this approach aims to create a more sustainable path toward improved health and weight regulation.

If you are struggling with persistent weight loss resistance, working with a practitioner at
Elemental Health & Nutrition
may help clarify contributing factors and guide appropriate next steps.

References

1. Earthman CP, Beckman LM, Masodkar K, Sibley SD. The link between obesity and low circulating 25-hydroxyvitamin D concentrations: considerations and implications. Int J Obes. 2012;36(3):387–396.
2. Barbagallo M, Dominguez LJ. Magnesium and metabolic disorders. Curr Pharm Des. 2010;16(7):823–833.
3. Zimmermann MB. Iodine deficiency. Endocr Rev. 2009;30(4):376–408.
4. Haas JD, Brownlie T. Iron deficiency and reduced work capacity: a critical review of the research. J Nutr. 2001;131(2S-2):676S–688S.
5. Hotamisligil GS. Inflammation and metabolic disorders. Nature. 2006;444(7121):860–867.
6. Gropper SS, Smith JL, Carr TP. Advanced Nutrition and Human Metabolism. 7th ed. Cengage Learning; 2018.
7. Rosen ED, Spiegelman BM. What we talk about when we talk about fat. Cell. 2014;156(1–2):20–44.
8. Wimalawansa SJ. Vitamin D in the new millennium. Curr Osteoporos Rep. 2012;10(1):4–15.
9. Hruby A, Meigs JB, O’Donnell CJ, Jacques PF, McKeown NM. Higher magnesium intake reduces risk of impaired glucose and insulin metabolism. Diabetes Care. 2014;37(2):419–427.
10. Costello RB, Rosanoff A, Dai Q, et al. Perspective: characterization of dietary supplements containing magnesium. Adv Nutr. 2016;7(1):199–215.
11. Taylor PN, Albrecht D, Scholz A, et al. Global epidemiology of hyperthyroidism and hypothyroidism. Nat Rev Endocrinol. 2018;14(5):301–316.
12. Pearce EN, Lazarus JH, Moreno-Reyes R, Zimmermann MB. Consequences of iodine deficiency and excess in pregnant women. Lancet Diabetes Endocrinol. 2016;4(6):538–550.
13. Beard J, Tobin B. Iron status and exercise. Am J Clin Nutr. 2000;72(2 Suppl):594S–597S.
14. McClung JP, Murray-Kolb LE. Iron nutrition and premenopausal women. J Trace Elem Med Biol. 2013;27(2):83–90.
15. Obermeyer CM, Bottiglieri T. Methylation and metabolism. Am J Clin Nutr. 2012;95(1):189–198.
16. Stover PJ. One-carbon metabolism–genome interactions in folate-associated pathologies. J Nutr. 2009;139(12):2402–2405.