What is a Plant-based Diet?
A plant-based diet primarily focuses on consuming whole foods derived from plants. This includes fruits, vegetables, nuts, seeds, oils, whole grains, legumes, and beans. The key aspect of a plant-based diet is its flexibility; it does not necessarily exclude animal products. The emphasis is on incorporating more plant foods into one's diet for their health benefits, such as reducing the risk of chronic diseases, improving heart health, and aiding in weight management. Most people who identify as eating a "plant based diet" focus on eating the whole plant, rather than segments, or a minimally processed version of it. Technically, mushrooms and yeast aren't "plants" since they belong to the Fungi Kingdom, but these foods are eaten by people who follow a "plant-based diet".
Veganism goes a step further than a plant-based diet by strictly avoiding all animal products. This means no meat, dairy, eggs, or any other products derived from animals, including honey and gelatin. Veganism is often adopted not only for assumed health reasons but also for ethical and environmental concerns. While a well-planned vegan diet can provide many health benefits, it can also lead to nutritional deficiencies if not properly managed. Common deficiencies among vegans include vitamin B12, iron, calcium, and omega-3 fatty acids.
Vegetarianism is another diet that excludes meat, but unlike veganism, it allows for the consumption of animal byproducts such as dairy and eggs. There are different types of vegetarian diets, including lacto-vegetarian (includes dairy), ovo-vegetarian (includes eggs), and lacto-ovo vegetarian (includes both dairy and eggs). While vegetarian diets can be healthier than diets high in animal products, they can still lead to some nutritional deficiencies, similar to vegan diets. For example, vegetarians may need to pay attention to their intake of vitamin B12, iron, and omega-3 fatty acids .
Veganism goes a step further than a plant-based diet by strictly avoiding all animal products. This means no meat, dairy, eggs, or any other products derived from animals, including honey and gelatin. Veganism is often adopted not only for assumed health reasons but also for ethical and environmental concerns. While a well-planned vegan diet can provide many health benefits, it can also lead to nutritional deficiencies if not properly managed. Common deficiencies among vegans include vitamin B12, iron, calcium, and omega-3 fatty acids.
Vegetarianism is another diet that excludes meat, but unlike veganism, it allows for the consumption of animal byproducts such as dairy and eggs. There are different types of vegetarian diets, including lacto-vegetarian (includes dairy), ovo-vegetarian (includes eggs), and lacto-ovo vegetarian (includes both dairy and eggs). While vegetarian diets can be healthier than diets high in animal products, they can still lead to some nutritional deficiencies, similar to vegan diets. For example, vegetarians may need to pay attention to their intake of vitamin B12, iron, and omega-3 fatty acids .
What Vegetables are Best?
The benefits from vegetable consumption may vary between certain groups of vegetables. Researchers have observed a significant inverse association with various cancers [bladder cancer (Michaud et al., 1999) and prostate cancer (Kirsh et al., 2007)] and the consumption of cruciferous vegetables, compared to total vegetable consumption.
Cruciferous vegetables are just one of the many groups of vegetables that are beneficial to human health. Ideally it is best to consume a variety of foods as no single food can provide all the nutrients, in the proper amounts, for optimal health.
Influence on Health
Among the leading causes of death in the United States, chronic degenerative diseases such as heart disease, cancer and diabetes may be prevented with a change in diet. Researchers continue to uncover what has long been known, that consuming a diet rich in vegetables, fruits, nuts and seeds promotes optimal health. Consuming a balance of plant-based foods that are nutrient-dense, rather than energy dense can significantly reduce morbidity and ultimately mortality.
|
Image by CDC from Health United States, 2015 Table 19
|
Influence on Inflammation
Researchers have observed a significant inverse association between inflammation and the consumption of cruciferous vegetables within studies conducted on animals. More recently, researchers evaluated the association between circulating levels of inflammation and the consumption of cruciferous vegetables in humans.
Participants that were analyzed included over 1000 females from the Shanghai Women’s Health Study (SWHS). A baseline survey and questionnaire was conducted to obtain data on anthropometric measurements, demographics, diet intake, lifestyle habits, medical history and other characteristics. In addition, biospecimens were collected to measure inflammatory [tumor necrosis factor- α (TNF- α), interleukin-1β (IL-1β) and IL-6] and oxidative stress [F2-isoprostanes (F2-IsoP); 2,3-dinor-5,6-dihydro-15-F2t-IsoP (F2-IsoP-M)] markers, from blood and urine, respectively.
Dietary intake was assessed using the food frequency questionnaire (FFQ), which has been indicated to be a valid and reproducible measure of food group intake. Vegetable groups included cruciferous vegetables (kale, collard greens, cabbage, broccoli, cauliflower, and bok choy), green leafy vegetables, allium vegetables (garlic, garlic sprouts, onions) and legumes. Participants were asked how often (e.g., daily, weekly, monthly, yearly or never), on average, they had consumed a specific food group.
The researchers discovered that a higher intake of cruciferous vegetables was associated with significantly lower circulating concentrations of proinflammatory markers. A similar, but less evident, inverse association was observed with the intake of all vegetables combined but not with noncruciferous vegetables. No statistically significant association was observed between oxidative stress markers and intake of vegetables, a phenomenon seen in many epidemiological studies. These results accounted for potential confounding variables such as socioeconomic status, dietary and nondietary lifestyle factors, BMI, health conditions and medication use. The evidence provided in this study supports the recommendation to increase consumption of cruciferous vegetables to reduce levels of inflammation.
Heart Disease and cancer
Researchers have evaluated the association between consumption of cruciferous vegetables and cardiovascular disease (CVD).
Data was analyzed from 2 studies conducted in China – the Shanghai Women’s Health Study (SWHS) and the Shanghai Men’s Health Study (SMHS). Participants that were analyzed in the SWHS included over 73,000 women between the ages of 40-70 years from 7 urban communities in Shanghai. Participants that were analyzed in the SMHS included over 61,000 men between the ages of 40-74 years from the same communities. Data on anthropometric measurements, demographics, diet, lifestyle habits, medical history and other factors was obtained via interviews.
Similar to the methods of Dietary intake was assessed using the food frequency questionnaire (FFQ), which has been indicated to be a valid and reproducible measure of food group intake. Vegetable groups included cruciferous vegetables, green leafy vegetables, allium vegetables and legumes. Participants were asked how often, on average, that he or she had consumed a specific food group.
Participants were followed via home visits and records from several registries to analyze deaths from all causes. Information on death certificates was used to determine the cause of death, a valid method of measuring rates of CVD and cancer.
In both men and women, individuals with a higher total fruit and vegetable consumption tended to be younger with higher education, occupational status and family income, as well as a a higher frequency of exercise. Of the identified deaths between the groups, fruit and vegetable consumption, especially cruciferous vegetable consumption, was inversely associated with risk of total mortality. Compared to total mortality, a stronger inverse relationship was observed between the risk of CVD mortality, in both men and women, and the consumption of total vegetables, especially cruciferous vegetables. Cruciferous vegetables are uniquely characterized by their high content of glucosinolates. Glucosinolates are sulfur-containing compounds that are suggested to provide anti-inflammatory effects and protection against certain cancers.
These findings support the recommendation to increase consumption of fruits and vegetables, particularly cruciferous vegetables, to promote cardiovascular health and overall longevity.
Data was analyzed from 2 studies conducted in China – the Shanghai Women’s Health Study (SWHS) and the Shanghai Men’s Health Study (SMHS). Participants that were analyzed in the SWHS included over 73,000 women between the ages of 40-70 years from 7 urban communities in Shanghai. Participants that were analyzed in the SMHS included over 61,000 men between the ages of 40-74 years from the same communities. Data on anthropometric measurements, demographics, diet, lifestyle habits, medical history and other factors was obtained via interviews.
Similar to the methods of Dietary intake was assessed using the food frequency questionnaire (FFQ), which has been indicated to be a valid and reproducible measure of food group intake. Vegetable groups included cruciferous vegetables, green leafy vegetables, allium vegetables and legumes. Participants were asked how often, on average, that he or she had consumed a specific food group.
Participants were followed via home visits and records from several registries to analyze deaths from all causes. Information on death certificates was used to determine the cause of death, a valid method of measuring rates of CVD and cancer.
In both men and women, individuals with a higher total fruit and vegetable consumption tended to be younger with higher education, occupational status and family income, as well as a a higher frequency of exercise. Of the identified deaths between the groups, fruit and vegetable consumption, especially cruciferous vegetable consumption, was inversely associated with risk of total mortality. Compared to total mortality, a stronger inverse relationship was observed between the risk of CVD mortality, in both men and women, and the consumption of total vegetables, especially cruciferous vegetables. Cruciferous vegetables are uniquely characterized by their high content of glucosinolates. Glucosinolates are sulfur-containing compounds that are suggested to provide anti-inflammatory effects and protection against certain cancers.
These findings support the recommendation to increase consumption of fruits and vegetables, particularly cruciferous vegetables, to promote cardiovascular health and overall longevity.
China study limitations
Not to discredit "The China Study" by T. Colin Campbell and Thomas M. Campbell, as it has been influential in promoting a plant-based diet. However, it has faced several criticisms from various experts.
Critics argue that the study, like many epidemiological studies, relies heavily on observational data, which can only show correlation, not causation. Just because two variables are correlated does not mean one causes the other. With this, some have accused the authors of selectively using data to support their conclusions while ignoring data that might contradict their thesis. It is easy to cherry-pick data to make any behavior result in any result.
The study has been criticized for oversimplifying complex relationships between diet and disease. Critics argue that nutrition and health outcomes are influenced by a multitude of factors, and reducing these relationships to a single cause (animal protein) is overly simplistic. Something to keep in mind is that the study did not differentiate the quality or type of animal product consumed. In other words, burgers from McDonalds could be considered nutritionally the same as pasture-raised beef. Of course, there are vast differences in metabolites between these two animal products, despite them both being animal products.
Furthermore, the study focuses primarily on the intake of animal protein and dairy, potentially ignoring other important nutrients and lifestyle factors such as physical activity, smoking, and other dietary components that can significantly impact health. A well recognized confounding variable is the "healthy user bias," which is is a type of selection bias that occurs when the subjects of a study are not representative of the general population because they engage in behaviors that are generally healthier. This can lead to skewed results because the outcomes being measured are influenced by factors other than the variable being studied.
As it relates to The China Study which compares the health outcomes of people who consume plant-based foods versus those who consume animal-based foods. Those who choose a plant-based diet may also engage in other health-promoting behaviors such as regular exercise, avoiding smoking, and having regular medical check-ups. These additional healthy behaviors can lead to better health outcomes, which might then be incorrectly attributed solely to their diet.
On the other hand, individuals who consume more animal-based foods might engage in fewer health-promoting behaviors. They might exercise less, have higher rates of smoking and alcohol consumption, and lower socioeconomic status, all of which can negatively impact health outcomes.
The observed health benefits attributed to plant-based diets in the China Study could be partially due to these other health behaviors rather than the diet alone. This illustrates how healthy user bias can potentially confound the results of dietary studies.
To address healthy user bias, researchers can design the study before-hand as a randomized controlled trial (RCT). This can help ensure that the groups being compared are similar in all respects except for the intervention being studied.
Healthy user bias is a critical consideration in interpreting the results of observational studies like the China Study. While plant-based diets might certainly offer significant health benefits, the extent of these benefits can be influenced by other health-promoting behaviors commonly practiced by individuals adhering to such diets. Recognizing and accounting for this bias is essential for accurately understanding the relationship between diet and health outcomes.
These criticisms suggest that while "The China Study" has contributed to the discussion on diet and health, its conclusions should be considered in the context of its limitations and the broader body of nutritional science.
Critics argue that the study, like many epidemiological studies, relies heavily on observational data, which can only show correlation, not causation. Just because two variables are correlated does not mean one causes the other. With this, some have accused the authors of selectively using data to support their conclusions while ignoring data that might contradict their thesis. It is easy to cherry-pick data to make any behavior result in any result.
The study has been criticized for oversimplifying complex relationships between diet and disease. Critics argue that nutrition and health outcomes are influenced by a multitude of factors, and reducing these relationships to a single cause (animal protein) is overly simplistic. Something to keep in mind is that the study did not differentiate the quality or type of animal product consumed. In other words, burgers from McDonalds could be considered nutritionally the same as pasture-raised beef. Of course, there are vast differences in metabolites between these two animal products, despite them both being animal products.
Furthermore, the study focuses primarily on the intake of animal protein and dairy, potentially ignoring other important nutrients and lifestyle factors such as physical activity, smoking, and other dietary components that can significantly impact health. A well recognized confounding variable is the "healthy user bias," which is is a type of selection bias that occurs when the subjects of a study are not representative of the general population because they engage in behaviors that are generally healthier. This can lead to skewed results because the outcomes being measured are influenced by factors other than the variable being studied.
As it relates to The China Study which compares the health outcomes of people who consume plant-based foods versus those who consume animal-based foods. Those who choose a plant-based diet may also engage in other health-promoting behaviors such as regular exercise, avoiding smoking, and having regular medical check-ups. These additional healthy behaviors can lead to better health outcomes, which might then be incorrectly attributed solely to their diet.
On the other hand, individuals who consume more animal-based foods might engage in fewer health-promoting behaviors. They might exercise less, have higher rates of smoking and alcohol consumption, and lower socioeconomic status, all of which can negatively impact health outcomes.
The observed health benefits attributed to plant-based diets in the China Study could be partially due to these other health behaviors rather than the diet alone. This illustrates how healthy user bias can potentially confound the results of dietary studies.
To address healthy user bias, researchers can design the study before-hand as a randomized controlled trial (RCT). This can help ensure that the groups being compared are similar in all respects except for the intervention being studied.
Healthy user bias is a critical consideration in interpreting the results of observational studies like the China Study. While plant-based diets might certainly offer significant health benefits, the extent of these benefits can be influenced by other health-promoting behaviors commonly practiced by individuals adhering to such diets. Recognizing and accounting for this bias is essential for accurately understanding the relationship between diet and health outcomes.
These criticisms suggest that while "The China Study" has contributed to the discussion on diet and health, its conclusions should be considered in the context of its limitations and the broader body of nutritional science.
References
Jiang, Y., Wu, S., Shu, X., Xiang, Y., Ji, B., Milne, G., … Yang, G. (2014). Cruciferous vegetable intake is inversely correlated with circulating levels of proinflammatory markers in women. Journal of the Academy of Nutrition and Dietetics., 114(5), 700–8. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/24630682
Kirsh, V., Peters, U., Mayne, S., Subar, A., Chatterjee, N., Johnson, C., … Prostate (2007). Prospective study of fruit and vegetable intake and risk of prostate cancer. Journal of the National Cancer Institute., 99(15), 1200–9. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/17652276
Michaud, D., Spiegelman, D., Clinton, S., Rimm, E., Willett, W., & Giovannucci, E. (1999). Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort. Journal of the National Cancer Institute., 91(7), 605–13. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/10203279
Zhang, X., Shu, X.-O., Xiang, Y.-B., Yang, G., Li, H., Gao, J., … Zheng, W. (2011). Cruciferous vegetable consumption is associated with a reduced risk of total and cardiovascular disease mortality. The American Journal of Clinical Nutrition, 94(1), 240–246. http://doi.org/10.3945/ajcn.110.009340
Kirsh, V., Peters, U., Mayne, S., Subar, A., Chatterjee, N., Johnson, C., … Prostate (2007). Prospective study of fruit and vegetable intake and risk of prostate cancer. Journal of the National Cancer Institute., 99(15), 1200–9. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/17652276
Michaud, D., Spiegelman, D., Clinton, S., Rimm, E., Willett, W., & Giovannucci, E. (1999). Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort. Journal of the National Cancer Institute., 91(7), 605–13. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/10203279
Zhang, X., Shu, X.-O., Xiang, Y.-B., Yang, G., Li, H., Gao, J., … Zheng, W. (2011). Cruciferous vegetable consumption is associated with a reduced risk of total and cardiovascular disease mortality. The American Journal of Clinical Nutrition, 94(1), 240–246. http://doi.org/10.3945/ajcn.110.009340
