An ovo-lacto vegetarian diet excludes meat, poultry, and fish but keeps eggs and dairy products on the table. It is the most common form of vegetarianism worldwide and the one with the deepest body of research behind it. Large cohort studies consistently link it to lower rates of heart disease, type 2 diabetes, and certain cancers, though the pattern also creates real nutritional gaps that need deliberate attention. How big those benefits are, and what trade-offs come with the territory, depends on what actually ends up on the plate.
Heart Health and Blood Pressure
The cardiovascular case for an ovo-lacto vegetarian diet is one of the better-supported claims in nutrition research. Studies consistently find that people following this pattern carry a more favorable cholesterol profile than omnivores. Both men and women show lower levels of LDL cholesterol (the kind linked to artery-clogging plaque) and better ratios between protective and harmful cholesterol fractions.1Nutrition Research. Lipoproteins and other clinical-chemistry parameters under the conditions of lacto-ovo-vegetarian nutrition In a controlled dietary trial called CARDIVEG, both a vegetarian and a Mediterranean diet produced meaningful improvements in body composition and blood lipids, suggesting that the benefit comes partly from the overall pattern of eating more plants and less saturated fat.2PubMed Central. Effects of a dietary intervention with lacto-ovo-vegetarian and Mediterranean diets on apolipoproteins and inflammatory cytokines: results from the CARDIVEG study
Blood pressure responds too. A meta-analysis of controlled trials found that people placed on a lacto-ovo vegetarian diet saw their systolic blood pressure drop by about 5 mmHg and diastolic by about 2.5 mmHg compared with other diets.3PubMed Central. Plant-Based Diets Reduce Blood Pressure: A Systematic Review of Recent Evidence Those numbers sound modest, but at a population level a sustained drop of even a few points in systolic pressure translates into meaningfully fewer strokes and heart attacks over time.
Diabetes and Metabolic Health
Type 2 diabetes is one area where the data on ovo-lacto vegetarianism looks particularly strong. In the Adventist Health Study-2, which tracked tens of thousands of people over several years, new diabetes cases turned up in about 1% of lacto-ovo vegetarians compared with roughly 2% of non-vegetarians. After adjusting for age, weight, exercise, and other lifestyle factors, lacto-ovo vegetarians still had about 38% lower odds of developing diabetes.4PubMed Central. Vegetarian diets and incidence of diabetes in the Adventist Health Study-2 Vegans fared even better, but the lacto-ovo group still showed a substantial and independent reduction.
Insulin sensitivity, the body’s ability to respond efficiently to its own insulin, also appears to improve. A case-control study of female Buddhists found that ovo-lacto vegetarians had lower insulin resistance scores and a reduced risk of metabolic syndrome compared with non-vegetarians, even after accounting for waist circumference and blood sugar.5PLoS ONE. Reduced Risk for Metabolic Syndrome and Insulin Resistance Associated with Ovo-Lacto-Vegetarian Behavior in Female Buddhists: A Case-Control Study A crossover feeding trial in older adults confirmed the pattern from the other direction: when participants were placed on a minimally processed lacto-ovo vegetarian diet, they lost weight and visceral fat, and their insulin sensitivity improved, much as it did when the same participants ate a minimally processed omnivorous diet.6PubMed. Impacts of minimally-processed omnivorous vs lacto-ovo-vegetarian diets on insulin sensitivity, lipid profile, and adiposity in older adults: Secondary findings from a randomized crossover feeding trial The takeaway is that a well-planned lacto-ovo vegetarian diet can be a genuine tool for metabolic health, though the quality of the food matters at least as much as the category.
Cancer Risk
Cancer research is messier than heart disease research because different cancer types have different drivers. Still, the largest studies available lean in the same direction. In the Adventist Health Study-2 cohort, vegetarians taken as a group had about 12% lower overall cancer incidence than non-vegetarians. Colorectal cancer stood out with a roughly 21% reduction, and stomach and lymphoproliferative cancers also appeared less frequently.7PubMed Central. Longitudinal associations between vegetarian dietary habits and site-specific cancers in the Adventist Health Study-2 North American cohort
When researchers isolated lacto-ovo vegetarians specifically, the signal for gastrointestinal cancers was strongest, with about a 25% lower risk compared with non-vegetarians.8Cancer Epidemiology, Biomarkers & Prevention. Vegetarian Diets and the Incidence of Cancer in a Low-risk Population For colorectal cancer on its own, lacto-ovo vegetarians showed an 18% reduction that fell just short of statistical significance, while pescatarians (who add fish) saw a stronger and clearly significant reduction.9JAMA Internal Medicine. Vegetarian Dietary Patterns and the Risk of Colorectal Cancers The pattern suggests real benefit, though it is hard to say how much comes from avoiding red and processed meat versus eating more fiber, or some combination.
Where the Nutrients Get Thin
The health benefits of an ovo-lacto vegetarian diet don’t come for free. Several nutrients require deliberate attention, and the ones most often in short supply are vitamin B12, iron, zinc, and omega-3 fatty acids.
Vitamin B12
B12 is produced by bacteria and concentrated in animal tissues, so it is far more abundant in meat and fish than in eggs or dairy. Ovo-lacto vegetarians get some B12 from their diet but often not enough over the long haul. In a study of pregnant women, about 25% of ovo-lacto vegetarians showed the combination of low B12 and elevated homocysteine (a marker of functional B12 shortage) in at least one trimester, compared with roughly 3% of meat-eating controls.10The Journal of Nutrition. Long-Term Ovo-Lacto Vegetarian Diet Impairs Vitamin B-12 Status in Pregnant Women Among younger adults outside of pregnancy, the picture is somewhat brighter: a recent European study found that the overall risk of actual B12 deficiency across diet groups, including lacto-ovo vegetarians, was low, though a small fraction still had elevated markers of insufficiency.11PubMed Central. Micronutrient intake and status in young vegans, lacto-ovo-vegetarians, pescatarians, flexitarians, and omnivores The bottom line: B12 supplementation or B12-fortified foods are a sensible insurance policy for anyone on this diet long-term, and they become critical during pregnancy.
Iron
Plants contain iron, but it is the non-heme form, which the body absorbs less efficiently than the heme iron found in meat. Compounds in whole grains, legumes, and tea (fiber, phytates, tannins) further reduce absorption. In a study of lacto-ovo vegetarian immigrants to Canada, iron deficiency rates were about 33% among women and 5% among men, with anemia following a similar pattern. The high prevalence in women was tied to low available iron intakes combined with heavy consumption of fiber and phytate-rich foods.12The American Journal of Clinical Nutrition. Iron status of predominantly lacto-ovo vegetarian East Indian immigrants to Canada: a model approach Practical strategies to boost iron absorption include eating vitamin C-rich foods alongside iron sources, cooking in cast iron, and soaking or sprouting legumes and grains to reduce their phytate content.
Zinc
Zinc follows a similar story. The same phytates and calcium that block iron absorption also interfere with zinc uptake, and the effect can be compounded in diets heavy on unleavened whole-grain breads and dairy. In a study of Asian immigrant vegetarians, about a third had low serum zinc levels, and the ratio of phytate to zinc in their diets was more than double that of omnivores.13Nutrition Research. Phytate:calcium:zinc ratios in Asian immigrant lacto-ovo vegetarian diets and their relationship to zinc nutriture That said, this is fixable. When a community of lacto-ovo vegetarian Trappist monks was reassessed a decade after initial concerns about their zinc status, their food choices had shifted toward lower-phytate options, and their plasma zinc had risen to upper-normal levels. The researchers concluded that adequate zinc nutrition is fully achievable on this diet with the right food knowledge.14Journal of the American Dietetic Association. Nutritional status and phytate:zinc and phytatex calcium:zinc dietary molar ratios of lacto-ovo vegetarian Trappist monks: 10 years later
Omega-3 Fatty Acids
The long-chain omega-3s EPA and DHA, found mainly in fatty fish, are nearly absent from an ovo-lacto vegetarian diet. In data from the Adventist Health Study-2, lacto-ovo vegetarians consumed an average of only about 18 mg per day of EPA and DHA, compared with about 117 mg for non-vegetarians and 158 mg for pescatarians. Their omega-3 index (a measure of these fats in red blood cell membranes) averaged around 3.9%, well below the 5% or higher level generally considered healthier.15PubMed Central. Dietary and erythrocyte PUFAs in vegan, lacto-ovo vegetarian, pesco-vegetarian, and non-vegetarian participants of the Adventist Health Study-2 Algae-based omega-3 supplements are the most straightforward way to close this gap without eating fish.
Bone Health
One area where vegetarian diets get a less flattering review is bone density and fracture risk. A 2024 review of large prospective studies found that vegetarian and especially vegan diets were associated with an increased risk of bone fractures. The authors attributed at least part of this risk to lower body weight and lower intakes of calcium, vitamin D, and protein.16PubMed. Risk of Bone Fracture on Vegetarian and Vegan Diets Ovo-lacto vegetarians have an advantage over vegans here because dairy products are rich in calcium, but the risk is still worth taking seriously. Getting enough vitamin D (through supplementation if sunlight exposure is limited) and keeping protein intake adequate are both important for protecting bones over the long term.
Protein, Muscle, and Athletic Performance
One of the most persistent worries about any vegetarian diet is whether you can get enough protein to build and maintain muscle. The evidence suggests you can, though it takes some effort. In a 12-week resistance training study, lacto-ovo vegetarians gained muscle mass and strength at rates that were statistically indistinguishable from meat-eaters, despite eating less total protein. Both groups consumed at least 1.2 grams of protein per kilogram of body weight per day.17PubMed. Similar body composition, muscle size, and strength adaptations to resistance training in lacto-ovo-vegetarians and non-vegetarians
A more recent randomized trial in older adults painted a slightly more nuanced picture. Both a vegetarian group and an omnivorous group gained appendicular (limb) muscle mass during resistance training, but the vegetarian group gained somewhat less, and the study could not formally establish that the vegetarian diet was non-inferior for muscle mass or total protein intake.18PubMed. Effects of a self-selected vegetarian vs. omnivorous diet on protein intake and muscle mass in older adults during resistance exercise: the IMPACT randomized controlled trial In other words, younger adults doing strength training seem to do fine on a lacto-ovo vegetarian diet as long as they hit a reasonable protein target, but older adults may need to be more intentional about protein-dense food choices or supplementation.
For endurance sports, a study of recreational runners found no differences in maximum power output or lactate levels during exercise testing among vegans, lacto-ovo vegetarians, and omnivores.19PubMed Central. Exercise capacity of vegan, lacto-ovo-vegetarian and omnivorous recreational runners A systematic review echoed this, concluding that a vegetarian diet did not negatively influence physical performance and that some vegetarian athletes even showed higher maximal oxygen consumption.20Research, Society and Development. How the vegetarian diet influences recreational and professional athletes’ physical performance: A systematic review
Pregnancy, Infants, and Growing Children
An ovo-lacto vegetarian diet during pregnancy does not appear to compromise basic birth outcomes. A study comparing lacto-ovo vegetarians, vegans, and omnivores found no significant differences in newborn length, head circumference, or BMI at birth.21PubMed. The impact of lacto-ovo-/lacto-vegetarian and vegan diets during pregnancy on the birth anthropometric parameters of the newborn Strict vegetarian (vegan) diets, by contrast, were linked to more than double the odds of delivering a small-for-gestational-age infant in a separate meta-analysis.22Metabolism Open. Strict vegetarian diet and pregnancy outcomes: A systematic review and meta-analysis The inclusion of eggs and dairy seems to provide enough of a nutritional buffer that this particular risk doesn’t carry over to the ovo-lacto pattern, though B12 monitoring is still critical, as noted earlier.
In children and adolescents, a systematic review and meta-analysis found that lacto-ovo vegetarians tended to be slightly leaner, with lower height, weight, and BMI z-scores and lower fat mass than omnivorous peers. Most nutrient levels stayed within pediatric reference ranges on average, but lacto-ovo vegetarian children had higher odds of iron deficiency and anemia, along with lower ferritin and vitamin D levels.23PubMed. Lacto-ovo-vegetarian and vegan diets in children and adolescents: a systematic review and meta-analysis of nutritional and health outcomes Pediatric diets on this pattern can work well, but they call for more attentive planning than the average family meal rotation provides.
Weight Management
Ovo-lacto vegetarians tend to weigh less than omnivores, but the reasons go beyond simply eating fewer calories. In the CARDIVEG trial, a vegetarian diet intervention produced a significant increase in adiponectin (a hormone associated with better fat metabolism) and a decrease in visfatin, while changes in leptin, insulin, and insulin resistance tracked closely with changes in body weight, BMI, and fat mass.24International Journal of Food Sciences and Nutrition. Effects of a dietary intervention with Mediterranean and vegetarian diets on hormones that influence energy balance: results from the CARDIVEG study In short, the hormonal environment seems to shift in a direction that favors leanness. But the crossover trial in older adults showed that both a minimally processed lacto-ovo vegetarian diet and a minimally processed omnivorous diet produced caloric reduction, weight loss, and visceral fat loss, suggesting that food quality matters as much as the vegetarian label.25PubMed. Impacts of minimally-processed omnivorous vs lacto-ovo-vegetarian diets on insulin sensitivity, lipid profile, and adiposity in older adults: Secondary findings from a randomized crossover feeding trial
Longevity and Overall Mortality
Whether vegetarian diets help you live longer is one of the most debated questions in nutrition. In the Adventist Health Study-2, lacto-ovo vegetarians had a roughly 9% lower risk of all-cause mortality compared with non-vegetarians after adjustment for confounders, and the reduction was particularly clear for cardiovascular death among men.26PubMed Central. Vegetarian Dietary Patterns and Mortality in Adventist Health Study 2 The confidence interval on that overall mortality finding, however, was right on the border of statistical significance, and the Adventist population is unusually health-conscious regardless of diet, which makes it hard to know how much of the benefit comes from the food itself versus the broader lifestyle.
Some researchers have argued that studies showing lower mortality in vegetarians may be substantially affected by healthy-user bias, the tendency for people who choose vegetarianism to also exercise more, smoke less, and drink less alcohol.27PubMed. Vegetarian diets for longevity: friend or foe? The honest read of the data is that a lacto-ovo vegetarian diet is probably mildly protective against premature death, but the effect is modest enough that confounders could be explaining some or even most of it.
Mental Health
The relationship between vegetarian diets and mental health is a surprisingly noisy area of research. A meta-analysis pooling ten studies found no association between a vegetarian diet and depression, and a separate pooled analysis of four studies found no link to anxiety either.28PubMed. Vegetarian diet and the risk of depression, anxiety, and stress symptoms: a systematic review and meta-analysis of observational studies But a competing meta-analysis reached a different conclusion, finding that vegetarians overall might face a higher risk of depression. When the researchers broke the data down by diet type, though, the elevated risk showed up only in semi-vegetarians and in Western populations. Lacto-ovo vegetarians specifically showed no significant association with depression.29Nutrition Reviews. Adherence to the vegetarian diet may increase the risk of depression: a systematic review and meta-analysis of observational studies The available evidence suggests that an ovo-lacto vegetarian diet neither reliably protects against nor promotes depression, and any link between plant-based eating and mood is likely driven by other factors like social isolation, disordered eating patterns, or nutrient deficiencies rather than the diet category itself.
The Gut Microbiome
Your diet substantially shapes the community of microbes in your gut, and an ovo-lacto vegetarian diet appears to produce a distinct microbial signature. Gene sequencing of gut bacteria in vegetarians and omnivores reveals significant differences in the types and proportions of bacterial families, genera, and species present.30PubMed. Lower Circulating Branched-Chain Amino Acid Concentrations Among Vegetarians are Associated with Changes in Gut Microbial Composition and Function These vegetarian-associated microbiomes were also linked to lower circulating levels of branched-chain amino acids, which at elevated concentrations have been implicated in insulin resistance and cardiometabolic disease. The microbiome is still a young field and cause-and-effect is hard to establish, but the data adds another plausible pathway through which this dietary pattern could influence metabolic health.
The Ultra-Processed Food Trap
Not all plant-based diets are created equal, and this is where a lot of people go wrong. Research on plant-based diet quality consistently shows that people who score high on an “unhealthy” plant-based diet index consume substantially more ultra-processed food, including sweetened beverages, refined grains, and sweets.31PubMed Central. The role of ultra-processed foods in plant-based diets: associations with human health and environmental sustainability Among young people, vegans actually got more of their energy from ultra-processed foods than lacto-ovo vegetarians or omnivores did, partly because plant-based meat and dairy substitutes are heavily processed by definition.32PubMed Central. Ultra-processed food intake and its nutritional consequences among youth when consuming vegan, lacto-ovo-vegetarian, pescatarian or omnivore diets: a cross-sectional study
Plant-based meat and dairy alternatives do offer some advantages over the animal products they replace: lower saturated fat, more fiber. But they also tend to contain less protein and lower levels of certain micronutrients.33Scientific Reports. Ultra-processed foods and plant-based alternatives impair nutritional quality of omnivorous and plant-forward dietary patterns in college students Ovo-lacto vegetarians have a natural advantage here because they can lean on actual eggs, yogurt, cheese, and milk rather than relying on engineered substitutes. The evidence strongly suggests that a vegetarian diet built around whole foods and minimally processed staples produces better health outcomes than one assembled from packaged convenience products, regardless of whether it technically avoids meat.
Environmental Footprint
For many people, the environmental argument is as important as the health one. A study comparing the carbon footprint, water footprint, and ecological footprint of omnivorous, ovo-lacto vegetarian, and vegan diets found that the omnivorous diet was substantially worse on every measure. The ovo-lacto vegetarian and vegan diets, interestingly, did not differ significantly from each other on environmental impact.34Scientific Reports. Environmental impact of omnivorous, ovo-lacto-vegetarian, and vegan diet This is encouraging for anyone who finds a fully vegan diet too restrictive: keeping eggs and dairy while cutting meat captures most of the environmental benefit. The bulk of the footprint difference comes from eliminating ruminant animals (cattle and sheep), whose production drives the highest greenhouse gas emissions and land use per calorie.