How strict vegan diets can lead to nutrient deficiency
Health & Science
By
Ayoki Onyango
| Nov 24, 2025
In a 2021 study of 150,000 vegans, Professor John Drawley of the University of California School of Public Health found that strict vegetarians consume larger quantities of food to meet their calorie needs.
They also spend significantly on non-animal-derived foods, which they eat in abundance. Samuel Maina, a nutritionist and lecturer at Kenya Medical Training College (KMTC) Nairobi campus, argues that concerns for animal welfare alone cannot justify avoiding products such as honey, eggs, milk, and blood, as these foods offer substantial health benefits.
“It is true that a plant-based diet can improve health and reduce the risk of certain conditions, such as skin problems, but ignoring honey, milk, meat, and eggs is at your own peril,” says Maina, a clinical health nutritionist and part-time lecturer at Karen College of Nutrition.
He adds that mild ailments like flu, the common cold, runny noses, and dry coughs can often be eased by taking a spoonful of honey mixed with hot lemon.
Dr Chris Ojiewo, a plant breeding expert and agricultural researcher with CIMMYT, now advises vegetarians to include animal products like milk, eggs, and small amounts of meat in their diets.
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“Animal products such as milk, eggs, and a bit of meat provide nutrients that would otherwise require consuming large quantities of plant-based foods, contrary to common vegetarians’ beliefs,” says Dr Ojiewo.
He adds that livestock-derived foods—meat, eggs, and milk—offer up to 12 times the nutritional value of vegetables and grains such as carrots, tomatoes, onions, and cereals.
According to Dr Ojiewo, ageing adults need certain livestock-derived foods to help preserve memory, maintain healthy bones, and retain muscle mass.
These foods are rich in essential bio-nutrients critical for growth and brain development. Amino acids in milk and eggs, for example, contain three times the nutrients found in staples like rice, maize, and wheat.
He notes that similar systematic trials and prospective studies from overseas universities, including research at the University of California, have shown that milk and other dairy products have no clear link to reducing cardiovascular risk or mortality.
Eggs and milk are also packed with micronutrients vital for cell division, growth, and membrane signalling. “While milk provides calcium, excessive intake may contribute to obesity,” adds Dr Ojiewo.
Nutritionists note that individuals who eat eggs, drink milk, consume cooked blood, and use honey are not pure vegans but ovo-vegetarians.
“Relying solely on plant-based foods can put one at risk of deficiencies in key nutrients such as protein, omega-3 fatty acids, and vitamins B12 and B2,” they explain.
They advise planning a diet that provides all essential nutrients to maintain overall health. Excessive intake of processed carbohydrates can lead to mineral deficiencies, particularly calcium, iron, and zinc, and may affect blood pressure, which should remain within a normal range.
A recent report in The Lancet indicates that the growth rates and related health outcomes of those on extreme vegetarian diets differ from those of vegetarians on less restrictive diets and from non-vegetarians.
Vitamin B12 and calcium supplements are essential for breastfed infants of vegan mothers. Studies show that iron deficiency and low iron stores are more common among vegans than non-vegetarians, as animal foods enhance iron absorption.
Research from various international universities also reports cases of rickets in vegetarian adolescents and osteoporosis in vegan lactating women with multiple pregnancies. Strict vegetarians may also lack vitamins A and C, increasing the risk of conditions like scurvy.