Introduction
In recent years, there has been a surge of interest in plant-rich diets, characterized by minimal or no consumption of animal-derived foods. This growing interest stems from the potential health advantages and environmental sustainability associated with these diets. As the global focus intensifies on mitigating climate change, with food production contributing significantly (approximately 20-30%) to global greenhouse gas (GHG) emissions, public health authorities are increasingly emphasizing plant-rich diets in their official recommendations. While the nutritional benefits of plant-rich diets are widely recognized, some uncertainty surrounds fully plant-based, or vegan diets, particularly concerning nutritional risks associated with lower bioavailability of certain amino acids in plant-based foods and reduced intake of nutrients predominantly found in animal foods. However, these risks can be easily mitigated through a diverse diet and/or the use of food supplements.
Understanding Omnivore Diets
An omnivore diet includes a wide range of food sources, from animal products like meat and dairy to plant-based foods. It is a dietary pattern that has been followed by humans for millennia, adapting to various environments and food availabilities. Omnivorous diets offer a broader spectrum of nutrients compared to more restrictive diets, potentially simplifying the process of meeting nutritional needs.
Nutrient Density
Advocates of omnivore-based diets emphasize the nutrient density of animal products, highlighting the completeness of proteins and essential vitamins crucial for human nutrition. Animal proteins are complete, containing all essential amino acids in the right ratios for human health. Vitamin B12 is naturally found in significant amounts in animal products. While plant sources contain iron and omega-3 fatty acids, the bioavailability from animal sources is generally higher.
Benefits of an Omnivore Diet
Omnivore diets can supply more quality complete proteins that are easily absorbed. A well-planned omnivore diet can provide all the necessary nutrients for optimal health. The protein found in meat is complete, high biological value protein, which means the proteins are more easily absorbed and utilized by the body. Meat products contain creatine and carnosine, which are beneficial to the brain and muscles. Meat has demonstrated the capacity to improve bone health, which is beneficial as humans grow older. Vitamin B12 is essential to prevention of pernicious anemia, which affects the central nervous system; thus an omnivore’s diet helps to protect the brain and nerves.
Meeting Nutritional Needs
One of the primary advantages of an omnivore diet is the ease with which it can meet the body's nutritional requirements. Animal products are rich sources of essential nutrients that can be more challenging to obtain in sufficient quantities from plant-based sources alone.
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Protein
Animal-based foods are complete proteins, meaning they contain all nine essential amino acids necessary for building and repairing tissues, producing enzymes and hormones, and supporting overall bodily functions.
Vitamin B12
Vitamin B12 is crucial for nerve function and red blood cell formation. It is primarily found in animal products, making it a nutrient of concern for those following a vegan diet.
Iron and Omega-3 Fatty Acids
While plant-based foods contain iron and omega-3 fatty acids, the forms found in animal products (heme iron and EPA/DHA omega-3s) are generally more bioavailable, meaning they are more easily absorbed and utilized by the body.
Risks of an Omnivore Diet
High intakes of meat and dairy are often linked to increased LDL cholesterol.
Potential for Unhealthy Choices
One of the main risks associated with an omnivore diet is the potential for making unhealthy food choices. An omnivore diet that heavily relies on processed foods, sugary drinks, and unhealthy fats can lead to various health problems.
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Increased Risk of Chronic Diseases
Studies have shown an increased incidence of chronic disease among those who eat meat. Today, meat and poultry are often treated with hormones to make the animals grow faster and larger, and antibiotics are used not only to treat, but also to prevent, disease. These methods concern for some consumers. High consumption of red and processed meats has been linked to an increased risk of heart disease, type 2 diabetes, certain cancers, and other chronic conditions.
Environmental Impact
The production of animal-based foods, particularly beef, has a significant environmental impact, contributing to greenhouse gas emissions, deforestation, and water pollution.
Comparing Omnivore and Vegan Diets: An Icelandic Study
To address the data gap, a study aimed to assess possible nutritional health risks and benefits among Icelandic vegans and omnivores. For that purpose, the compliance of both diets relative to official nutritional recommendations was assessed. In addition, the diet of both groups was characterized according to the proportion of energy from ultra-processed foods, which have received considerable attention as a possible determinant of several adverse health outcomes. Furthermore, the environmental sustainability of vegan versus omnivore diets was assessed in terms of dietary greenhouse gas emissions. The study used data on 651 omnivores and 15 vegans from the Icelandic National Dietary Survey conducted in 2019-2021 combined with data on 53 vegans recruited from a comparable study from 2022 to 2023 through the Icelandic Vegan Association.
Dietary Assessment
For both the National Dietary Survey and the vegan survey, the dietary assessment consisted of two 24-hour recalls and a short food frequency questionnaire to capture the habitual intake of common food groups. The two 24-hour recalls were conducted via phone by trained interviewers on two non-consecutive days, covering weekdays and weekends. Participants also answered several questions, encompassing demographic details, lifestyle, and health. Habitual dietary intake was estimated using the mean of two 24-hour recalls. The 24-hour recalls also recorded the use of dietary supplements.
Key Findings
Those following vegan diets were younger than omnivores (mean: 36 vs. 44 years) and more likely to be females (68% vs. 52%). Vegans also had slightly lower body mass index (BMI) than omnivores (23.7 vs. 26.9 kg/m2) and were more likely to have a university education compared to omnivores (75% vs. 52%). Most vegans (97%) and omnivores (72%) reported taking one or more food supplements. As expected, those following a vegan diet consumed more plant-rich food groups, including plant-based alternatives to animal-sourced foods. On a few recorded days (i.e., at the 90th percentile) some vegans reported minimal consumption of foods of animal origin including dairy, meat, and animal fats (i.e., lard and butter). The percentage of energy intake coming from ultra-processed foods was nearly identical (or ~ 46%) among vegans and omnivores. Vegans compared to omnivores were also more likely to meet the recommendation for the proportion of energy intake from carbohydrates, fibers, added sugars, total fat and saturated fat. Vegans, compared to omnivores, were less likely to meet protein recommendations both when expressed in terms of having protein intake equal to or above 10% of energy intake (82% vs. 99%) or when expressed as intake of ≥ 0.83 g protein/kg body weight (52% vs. 79%). After accounting for the intake of food supplements, the median intake of calcium (701 vs. 897 mg/day) and iodine (74 vs. 127 µg/day) were lower among vegans compared to omnivores and for vegans the median was in both cases below the AR. On the other hand, intake of vitamin C (174, vs. 82 mg/day), folate (484 vs. 296 µg/day) and iron (16.7 vd 9.7 mg/day ws substantially higher among vegans compared to omnivores. After adjustment for food loss up to retail level, the median total dietary GHG emissions from those adhering to vegan diet were 2.6 kg CO2-eq/ day (1.9, 4.2) compared to 5.3 kg CO2-eq/day (2.6, 10.8) for omnivores.
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Balancing the Omnivore Diet
To maximize the benefits and minimize the risks of an omnivore diet, it is essential to focus on balance and moderation. A well-balanced omnivore diet should include a variety of nutrient-dense foods from all food groups.
Prioritize Whole Foods
Emphasize whole, unprocessed foods such as fruits, vegetables, whole grains, lean proteins, and healthy fats.
Limit Processed Foods, Sugary Drinks, and Unhealthy Fats
Minimize the consumption of processed foods, sugary drinks, and foods high in saturated and trans fats.
Choose Lean Protein Sources
Opt for lean protein sources such as poultry, fish, beans, and legumes over red and processed meats.
Practice Portion Control
Be mindful of portion sizes to avoid overeating and maintain a healthy weight.
The Importance of Individualization
Nutrition is highly individualized and there is no “best diet” for everyone. It is also likely that the “best diet” lies somewhere in between the two options - a plant based diet that includes the occasional lean protein, seafood, egg, and low fat dairy options. The best diet for you is the one that allows you to eat more nutritious foods.
Health Goals
Consider your personal health goals when choosing between a plant-based and omnivore diet.
Nutritional Needs
Assess your individual nutritional needs and ensure that your chosen diet provides all the essential nutrients in adequate amounts.
Ethical Considerations
Take into account your ethical values and beliefs when making dietary choices.