For the last few weeks, and during the next ones, we are using the rubric More Info Mondays here on the blog to talk about some nutrients that can be critical for our health and that deserve a special attention, not only on a vegan or vegetarian diet, but for any kind of regimen.
This week we are talking about Zinc.
As selenium (from which we have talked before), zinc is also a essential mineral that belongs to the micronutrient group (along with vitamins and water) and is considered to be a trace mineral, since we only need very small amounts of it (contrary to, for instance, calcium or iron from which we need in bigger amounts).
Main functions of zinc:
Although it exists in our bodies in very small amounts (only 1.5 a 2 grams), zinc is present in every single cell of our body where it takes part in many important physiologic activities. Zinc functions are mainly related with the fact that zinc is a co-factor in more than 80 enzymes and metalloproteins and also as part of the DNA and RNA structure.
Zinc main functions are related to:
- Cellular division and growth.
- Fertility and reproductions, being essential for an healthy fetal development.
- Hormonal activity, since zinc interacts with many hormones, including insulin.
- Sexual maturation on teenagers.
- Night vision, since zinc is a key element on the activity of the enzyme that catalyzes vitamin A activation in the eye.
- Proper function of the immune system.
- Hemoglobin activity, since zinc increases its affinity to oxygen
- Fat metabolism.
- Protein metabolism.
- Genetic expression, since zinc takes part in important DNA structures that allow the transcription of genes into active proteins.
- Taste, olfact and appetite, since zinc participates in their regulation.
Regulation of the absorption of zinc:
The absorption of zinc from foods depends on:
- individual zinc levels at the moment,
- individual zinc needs at the moment,
- zinc content of the meal,
- intake of other mineral supplements (such as calcium and iron). On the other hand, the presence of these minerals on foods seems not to affect negatively the absorption of zinc, even in fortified foods.
- presence of phytates on foods, such as vegetables, nuts, seeds and cereals. Phytates bind to zinc and decrease its absorption. On the other hand, and contrary to what was thought, fiber does not impact negatively the absorption of this mineral.
Zinc deficiency can be manifested with:
Since zinc takes part in many physiologic activities, its deficiency can be manifested in many different ways and, given the lack of specificity of the symptoms, and it might be difficult to identify. The most common symptoms are slow growth and sexual maturation delay in children and teenagers, wound healing difficulty, hair loss, weak immune system with recurrent infections, dermatitis, acne, alterations in the palate, diarrhea, hypothyroidism and night vision impairment.
Besides vegetarians and vegans tend to have a lower intake of zinc comparing to people following "omnivore" diet, most studies do not find differences on blood zinc levels among the different diets. This can be explained by the fact that the body has the ability to adapt its zinc absorption to the amounts present in the diet. Even though, it is important to control regularly zinc levels through blood test and also be aware of any suspect symptom. In some circumstances (pregnant women, teenagers, men) supplementation might be needed.
The recommended daily allowance (RDA) of zinc varies with age and sex. The same way women have increased iron looses trough menstruation, men have higher zinc losses trough semen.
- Men: 13 mg
- Women: 11 mg
- 4-8 years old: 5 mg
- 9-13 years old: 9 mg
- 11-18 years old (boys): 11 mg
- 11-18 years old (girls): 9 mg
Food Sources of zinc
Although foods rich in animal protein (such as meat and seafood) are the main zinc source for most people in an "omnivore" diet, zinc is also present in considerable amounts in plant-based foods such as whole cereals, legumes, nuts and seeds.
- 1/2 cup oats (raw) - 3,1 mg (~39 % RDA)
- 1 cup cooked lentils - 2,5 mg (~31 % RDA)
- 1 cup cooked black beans - 1,8 mg (~22 % RDA)
- 1 cup cooked chickpeas - 1,3 mg (~13 % RDA)
- 1 cup cooked peas - 1,1 mg (~13 % RDA)
- 1/4 cup pumpkin seeds - 2,3 mg (~28 % RDA)
- 1/4 cup sunflower seeds - 1,8 mg (~22 % RDA)
- 1/4 cup almonds - 1,1 mg (~13 % RDA)
- 1/4 cup walnuts - 0,9 mg (~11 % RDA)
- 2 tbsp nutritional yest - 3,2 mg (~39 % RDA)
Including in your daily menu an oatmeal or a bowl with oat-based granola, a meal with a cup of cooked legumes and a handful of nuts and seeds is one of the possible strategies to attain your daily zinc intake.
Strategies to increase zinc absorption:
- sprout and ferment legumes, nuts and seeds to decrease their content in phytate.
- include in your meals acid-rich fruits (such as citric fruits, rich in citric acid, apples, rich in malic acid, and grapes, rich in tartaric acid), which bind to zinc and increase its absorption.
- combine foods that are rich in zinc with food rich in sulfur such as garlic and onions, which increase the absorption of zinc (and iron too).
Excess zinc can be toxic
Although the body can excrete the excess zinc with relative ease and the cases of zinc toxicity being relatively rare, they can happen eventually, specially in cases of chronic supplementation. Some symptoms of zinc toxicity are vomits, appetite loss, diarrhea, weak immune system, lipid profile alteration with low HDL and deficiency in copper due to competition with zinc. As so, zinc supplementation must be supervised by a health care provider.
1. Linhas de Orientação para uma Alimentação Vegetariana Saudável, Programa Nacional Para a Promoção da Alimentação Saudável, DGS, 2015.
2. Institute of Medicine (IOM), Food and Nutrition Board (FNB). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). The National Academies Press. Washington, DC. 2002/2005.
3. Insel P, Turner R, Ross D, Nutrition, 2nd Ed, Jones and Barlet Publishers, Sudbury MA, 2004.
5. Gautam S,, et al., Higher bioaccessibility of iron and zinc from food grains in the presence of garlic and onion. J Agric Food Chem. 2010 Jul 28;58(14):8426-9.