Plant-based diets have surged in popularity, lauded for their health benefits and positive environmental impact. Prospective studies suggest that consuming vegetarian diets is associated with a reduced risk of developing cardiovascular disease (CVD), diabetes, hypertension, dementia, and cancer. But, not all plant-based foods are equally healthy. Unhealthy vegetarian diets poor in specific nutrients (vitamin B12, iron, zinc, and calcium) and/or rich in highly processed and refined foods increase morbidity and mortality. It is important to consider the specific nutrients and health benefits of a meat and vegetable diet.
Understanding Plant-Based Diets
There are different types of plant-based diets, but in this review, we will focus our attention primarily on vegan (100% plant-based), lacto-ovo vegetarian (i.e. plant-based except for dairy products and/or eggs), and pesco-vegetarian or pescatarian (i.e. plant-based except for fish and seafood with or without eggs and dairy) diets. All vegetarian diets exclude meat (e.g. According to the American and Canadian Dietetic Associations, appropriately planned and supplemented vegan and lacto-ovo vegetarian diets are nutritionally adequate and suitable for individuals in all stages of the life cycle and may provide health benefits in disease prevention and treatment.
The Cardioprotective Mechanisms of Healthy Vegetarian Diets
Multiple nutritional effectors of a healthy vegetarian diet modulate important metabolic, hormonal, and immune factors associated with the development of cardio- and cerebrovascular diseases. Several factors can explain why vegetarians have significantly lower levels of plasma cholesterol, especially when they consume minimally processed plant foods. Vegetarians do not consume meat, and vegans also avoid milk, butter, and dairy. Beef, lamb, and pork contain high levels of saturated fat and cholesterol and minimal amounts of polyunsaturated fats; even lean cuts of beef may contain up to 4.5 g of saturated fat per 100 g serving. Epidemiological studies have shown a strong linear relationship between saturated fat intake, plasma cholesterol levels, and CHD. Substituting 5% of energy intake from saturated fatty acids with a similar quantity of energy from polyunsaturated fats, monounsaturated fats, or carbohydrates from whole grains is associated with a 25%, 15%, and 9% lower risk of CHD, respectively. However, when saturated fats are replaced with carbohydrates from refined carbohydrates, the risk of developing CHD increases substantially. Data from randomized clinical trials have demonstrated a cause-effect relationship; replacing saturated fat with vegetable polyunsaturated fats decreases CHD by 30% that is similar to the reduction induced by statin therapy. Seeds and nuts are excellent sources of polyunsaturated fatty acids and contain soluble and insoluble fibres and sterols that are known to lower cholesterol. Epidemiological studies suggest that frequent nut consumption can reduce the risk of CHD by 40%-60%. Data from randomized clinical trials confirm that consuming a diet rich in nuts, viscous fibres from oats, barley, psyllium, and plant sterol ester-enriched margarine can reduce plasma low-density lipoprotein (LDL) cholesterol by 13%. Moreover, vegetarian diets rich in whole grains, legumes, nuts, and dried fruits can provide ∼15 g of dietary fibre per 1000 kcal.
Weight Management
Vegetarians, and especially vegans, tend to have lower body weights than omnivores. In a survey of the American Adventists population, average body mass index (BMI) in omnivores, semi-vegetarians, lacto-ovo vegetarians, and vegans was 28.3, 27.3, 26.1, and 24.1 kg/m2, respectively. Although consuming a vegetarian diet does not require counting calories, results from clinical trials demonstrate that people randomized to a vegetarian diet tend to lose more weight than those consuming Western diets. The high-fibre and water content and lower energy density of vegetables, legumes, and whole grains may in part explain this effect. Consumption of diets rich in dietary fibre induces gastric distention, delays gastric emptying, and prevents large fluctuations in postprandial blood glucose. Short-chain fatty acids produced by the intestinal microbial metabolism of resistant starch and oligosaccharides of minimally refined plant foods induce satiety by inhibiting gastric emptying through incretins such as peptide-YY and glucagon like peptide-1 that markedly reduce blood glucose and body weight in randomized clinical trials. Moreover, whole-food vegan and vegetarian diets may result in fewer bioavailable calories, and it is well known that calorie restriction with adequate nutrition in humans exert a powerful effect in improving glucose tolerance, insulin sensitivity, and many other cardiometabolic, inflammatory, and hormonal factors implicated in the pathogenesis of CVD and cancer. As reviewed elsewhere, excessive (central) adiposity causes insulin resistance, dysregulation of sex hormones and insulin-like growth factor-1 (IGF-1) signalling, low-grade chronic inflammation, and immune dysregulation of natural killer cells and stromal tumour-infiltrating lymphocytes, limiting antitumour responses.
Insulin Sensitivity and Glucose Control
Additional mechanisms mediating the insulin sensitizing and glucose-lowering effects of healthful minimally processed vegetarian diets are the low glycaemic index/load and the lower intake of protein, especially of sulphur and branched-chain amino acids. Estimated daily protein intake for omnivores in Western societies is ∼90-100 g of which ∼70%-85% is animal proteins rich in methionine, valine, leucine, and isoleucine.
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The Power of Plant-Based Micronutrients and Phytochemicals
Well-designed vegetarian diets rich in vegetables, whole grains, legumes, nuts, seeds, and fruits provide a wide range of vitamins (vitamin C, vitamin E, and beta-carotene), minerals (selenium), and phytochemicals (tannins, phenols, alkaloids, and flavonoids) with xenohormetic effects. Numerous large observational studies suggest that an inverse relationship exists between antioxidant and polyphenol intake and the risk of developing diabetes, CVDs, cancer, and possibly dementia. High intake of dietary antioxidants and phytochemicals may reduce the risk of developing atherosclerotic plaques because it triggers adaptive modulations of stress-response enzymes and receptors that prevent lipoprotein oxidation, endothelial dysfunction, and immune activation.
Reducing Inflammation with Diet
Findings from large prospective studies suggest that dietary patterns with higher inflammatory potential are significantly associated with higher level of systemic and vascular inflammation, an unfavourable lipid profile, and ultimately with a higher incidence of CHD and stroke. Dietary patterns with lower inflammatory potential are those that favour foods rich in dietary antioxidants and vegetable fibre (e.g.
Blood Pressure Regulation
Diets rich in vegetable fibre, potassium, and magnesium and low in sodium, especially when associated with a healthy body weight and regular endurance exercise training, markedly lower systolic and diastolic blood pressure, which is a powerful risk factor for the development of CHD, heart failure, stroke (both ischaemic and haemorrhagic), and dementia.
Impact on Gut Microbiome
Diet composition has a pervasive effect in modulating systemic microbiome biology.
The Downside of Red Meat
Most Americans eat 1.5 times more protein than the recommended dietary allowance each day. High consumption of red and processed meat has been linked with chronic diseases, including heart disease, type 2 diabetes, obesity, and some cancers. Red and processed meats are higher in saturated fats and cholesterol than most other proteins. Animal products are the only source of dietary cholesterol; they are also the primary source of saturated fat in our diet, which is associated with higher blood cholesterol levels.
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Considerations for Meat Consumption
It is recommended that you do not eat too much red meat, processed meat or meat that is high in saturated fats as this can lead to health problems. Processed meat can also be high in salt and eating too much salt can increase your risk of high blood pressure. If you currently eat more than 90g (cooked weight) of red or processed meat a day, it is recommended that you cut down to 70g.
Making Healthier Choices with Meat
Making healthier choices can help you eat meat as part of a balanced diet. When buying meat, go for the leanest option. As a rule, the more white you can see on meat, the more fat it contains. It's important to store and prepare meat safely to stop bacteria from spreading and to avoid food poisoning: store raw meat or raw poultry in clean sealed containers on the bottom shelf of the fridge, so the meat cannot touch or drip onto other food follow any storage instructions on the label and do not eat meat after its "use by" date store red meat or raw poultry in a freezer before its "use by" date if you cook meat that you're not going to eat straight away, cool it as quickly as possible and then put it in the fridge or freezer - remember to keep cooked meat separate from raw meat and only reheat cooked meat once always thoroughly clean plates, utensils, surfaces and hands straight away after they have touched raw or thawing meat using warm soapy water or disinfectant cleaning products
Health Benefits of Reducing Meat Consumption
Consuming less red and processed meat and more plant-based foods such as vegetables, whole grains, beans, soy, and nuts can offer a variety of health benefits.
Heart Health
The risk factors for cardiovascular disease-which can increase the risk of heart attack and stroke-include eating a diet high in saturated fat, trans fat, and cholesterol. Eating more healthy plant-based meals can help people looking to reduce or manage their cholesterol levels.
Preventing Type 2 Diabetes
Approximately one in three American adults has prediabetes-a risk factor for developing type 2 diabetes. Eating a plant-rich diet with less meat can help lower the risk of developing type 2 diabetes. Skipping just one half serving of meat per day and replacing it with a plant protein (like beans or tofu) can help lower the risk of developing type 2 diabetes by 15%.
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Kidney Health
In the United States, about 30 million adults have chronic kidney disease-and most aren’t aware of it. One in three American adults are at risk for chronic kidney disease. Reducing consumption of red and processed meat and eating more healthy plant-based foods can help lead to better kidney health, management of kidney disease and a reduction in related risk factors.
Boosting Immunity
A healthy plant-based diet can help strengthen your immune system to aid in fighting viruses and help you recover more quickly from illness. Fruits and vegetables contain a broad spectrum of nutrients and phytochemicals that help minimize damage to cells and defend against harmful pathogens.
Weight Management
Maintaining a healthy weight can reduce the risk of serious health problems.
Navigating the Paleo Diet
A paleo diet is an eating plan based on foods humans might have eaten during the Paleolithic Era. A modern paleo diet includes fruits, vegetables, lean meats, fish, eggs, nuts and seeds. These are foods that in the past people could get by hunting and gathering. It doesn't include foods that became more common when small-scale farming began about 10,000 years ago.
Benefits and Concerns
In general, a paleo diet has many features of recommended healthy diets. Common features the paleo diet has include the emphasis on fruits, vegetables, lean meats and the avoidance of processed foods. The main concern about paleo diets is the lack of whole grains and legumes. These foods are considered good sources of fiber, vitamins, proteins and other nutrients. Also, low-fat dairy products are good sources of protein, calcium, vitamins and other nutrients. Whole grains, legumes and dairy also are generally more affordable and available than foods such as wild game, grass-fed animals and nuts. For some people, a paleo diet may be too costly.
The Impact of Vegetarian Diets on Chronic Diseases
Prospective epidemiological studies have suggested that consuming vegetarian diets might have protective effects against the development of obesity, diabetes, hypertension, CHD, several type of cancers, and, most recently, cognitive decline. Several studies suggest protective effects of vegetarian diets in the prevention of T2DM. Findings from the Adventist Health Study-2 (41 387 participants free of diabetes followed for 2 years) found that, even after controlling for multiple confounding factors, vegetarians had a significantly lower risk of T2DM than omnivores. The most apparent protective effect was for vegan diets with a 62% risk reduction, followed by semi-vegetarian (51% reduction) and lacto-ovo vegetarian (38% reduction) diets. The Adventist Mortality Study and Adventist Health Study followed a cohort of 8401 individuals for more than 17 years. After controlling for weight and weight change, long-term adherence to a diet incorporating weekly meat intake was associated with a 38% higher risk of T2DM compared with a vegetarian diet with no meat intake. This finding are supported by data from a joint analysis of three large cohort studies (the Health Professionals Follow-up Study, n = 26,357; the Nurses’ Health Study, n = 48,709; and the Nurses’ Health Study II, n = 74,077) confirming a statistically significant association between red meat consumption and an increased risk of T2DM (P < .001 for all studies). After adjusting for initial BMI and concurrent weight gain, a daily increase of > 0.5 servings of red meat was linked with a 30% higher risk of T2DM.
Cardiovascular Health and Mortality
A joint analysis of five prospective studies including 76 172 individuals has shown a lower CHD mortality in vegetarians than in omnivores: 34% less in lacto-ovo vegetarians and pesco-vegetarians and 26% lower in vegans. Another meta-analysis of 7 studies (124 706 participants) report a 29% decreased mortality from CHD in vegetarians than omnivores. The EPIC-Oxford cohort study (44 561 participants) showed a 32% risk reduction of CHD in vegetarians than non-vegetarians.
Cancer Prevention
A meta-analysis of 7 epidemiological studies (124 706 participants) found an 18% lower cancer incidence in vegetarians than omnivores {relative risk [RR]: 0.82 [95% confidence interval (CI): 0.67, 0.97]}. Results from the EPIC-Oxford study on a cohort of 65 000 men and women found that the overall cancer risk was 10% lower in vegetarians and 18% lower in vegans than in meat-eaters. Recent data from the UK Biobank prospective study on 409 110 participants show that compared with omnivores, vegetarians had a 13% and pescatarians a 7% lower overall cancer risk, respectively. In this study, vegetarians had a lower risk of colorectal and prostate cancer, and pescatarians had a lower risk of melanoma. However, when these data were pooled with eight previously published studies in a meta-analysis, only the association with colorectal cancer persisted. The incidence of lung cancer, for example, is lower in vegetarians than in people consuming typical Western diets, but this seems due primarily to the reduced smoking habit of vegetarians.
Addressing Nutritional Needs on a Vegetarian Diet
To get the most out of a vegetarian diet, choose a variety of healthy plant-based foods. These include whole fruits and vegetables and whole grains. Keep in mind that the more foods you cut out of your diet, the harder it can be to get all the nutrients you need.
Key Nutrients
Calcium helps build and maintain strong teeth and bones. Vitamin D also plays an important role in bone health. Vitamin B-12 is necessary to produce red blood cells and prevent anemia. Protein helps keep skin, bones, muscles and organs healthy. Omega-3 fatty acids are found in fish, canola oil, soy oil, walnuts, ground flaxseed and soybeans. Iron is important to red blood cells. Zinc helps the body make proteins and grow cells. Thyroid hormones are made partly of iodine.
Embracing Plant-Forward Eating
Plant-based or plant-forward eating patterns focus on foods primarily from plants. This includes not only fruits and vegetables, but also nuts, seeds, oils, whole grains, legumes, and beans. It doesn't mean that you are vegetarian or vegan and never eat meat or dairy. Plant-forward is a style of eating that includes meat. But meat is not the star of the meal. This kind of healthy eating is key to the Mediterranean diet. It's also key to other cuisines, such as some Asian, Ethiopian, Indian and Middle Eastern diets. These diets limit red meat. And they focus on fruits, vegetables, beans, peas, lentils, nuts, whole grains and healthy fat. This type of diet has been shown to lower the risk of heart disease and other chronic conditions.
Practical Tips for Incorporating More Vegetables
If you aren’t ready to give up meat but want to increase your intake of vegetables, there are plenty of ways to do so. Vegetable Juice: start your day with a juice or green smoothie packed with vegetables. Swap Lunch Meat for a Salad: the experts have been telling us for years that processed deli meats are bad for our health. Meat Free Monday: if you can’t bear the thought of giving up meat for good, swap your evening meal on Mondays to a vegetarian meal. Soups in Winter: warm up with a vegetable-based soup for lunch or dinner throughout winter.