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The Importance of Diet: Correlations with Diseases and Health
Chronic disease has become the leading cause of global health problems; however, it is increasingly recognized that dietary choices are one of the most important factors which can be modified to improve health. A large body of literature supports that poor dietary habits are linked to several common chronic diseases such as obesity, type II diabetes, heart disease, cancer, mental illness and that eating healthy reduces risk for all of these health-related issues. This article will explore the relationship between diet and chronic disease, by referencing the last decade’s research on the harmful effects of ultra-processed foods, as well as current scientific evidence-based guidelines for what constitutes a healthy diet.
The Perils of Ultra-Processed Foods
Ultra-processed foods make up an increasing percentage of what we eat today, and are defined by high levels of added sugars, salt, fats, and industrial additives (like those in soda, packaged snacks and ready meals i.e Ultra Processed Foods). They contribute between 42% and 58% of total dietary energy in high-income countries like the U.S., Australia and many others. Exposing oneself to greater amounts of ultra-processed foods has been shown to be associated with negative health effects in numerous areas, such as: increased risk of mortality, increased risk of various forms of cardiometabolic diseases, increased risk of cancer, and various mental health complications. The relationship between consuming ultra-processed foods and developing type 2 diabetes is also supported by strong scientific evidence. Specifically, research shows that a 10% increase in ultra-processed food intake is associated with a 12% greater risk of developing type 2 diabetes. Additionally, studies have found strong correlations between consuming ultra-processed foods and both obesity (55% higher odds), and cardiovascular mortality (50% higher risk) when controlling for general diet quality. Research suggests that the mechanisms through which ultra-processed foods negatively affect our health include chronic inflammation, disruption of the gastrointestinal microbiota, and potential contaminants present in processed foods. Therefore, replacing ultra-processed foods with whole or minimally processed foods is critical to preventing disease.
https://www.bmj.com/content/384/bmj-2023-077310
Diet’s Role in Obesity and Metabolic Disorders
Approximately 70% of U.S. adults have been diagnosed with obesity, which is a chronic condition, but also has the potential to lead to other conditions such as diabetes and cardiovascular disease. The increased caloric intake from diets high in ultra processed foods contribute to weight gain (in some cases contributing an additional 500 calories per day), in addition to the low nutrient content found within those foods. On the flip side, eating a balanced diet consisting of fruits, vegetables, whole grains and lean protein will result in a lower prevalence rate for obesity. Using probiotics and plant-based foods to modulate the gut microbiome will help reduce the risk of developing metabolic syndrome; metabolic syndrome consists of several health-related conditions, including high blood pressure and elevated glucose levels. Maintaining a healthy body mass index during adulthood has the ability to potentially prevent approximately 73% of all non-alcoholic fatty liver disease cases, thus illustrating the role that diet plays in preventing certain diseases.
https://pmc.ncbi.nlm.nih.gov/articles/PMC6328339
https://www.bmj.com/content/384/bmj-2023-077310
https://pmc.ncbi.nlm.nih.gov/articles/PMC9921002
Correlations with Diabetes and Cardiovascular Disease
Highly processed foods are linked to increased Type 2 diabetes risk. A non-dose-response analysis suggests that highly processed food consumption increases the risk of developing Type 2 diabetes by about 40%. Plant-based diets can improve risk for Type 2 diabetes, especially when an individual may have genetic risk factors. Trials, such as PREDIMED, have shown that a Mediterranean diet that includes high amounts of olive oil, nuts, and fish can decrease the risk of Type 2 diabetes by about 40%. Additionally, there are also several patterns related to cardiovascular disease such as the DASH (Dietary Approaches to Stop Hypertension) and Alternate Healthy Eating Index (AHEI) which are both associated with 15-25% less risk of experiencing cardiovascular events (heart attack/stroke). Studies show that greater adherence to scores of the Alternate Mediterranean Diet (AMED) were associated with a 6% decreased risk of cardiovascular disease per quintile increase. The health benefits associated with these diets can be attributed to the improvement of lipid profiles, inflammation levels, and blood pressure management.
https://www.bmj.com/content/384/bmj-2023-077310
https://pmc.ncbi.nlm.nih.gov/articles/PMC9921002
https://www.bmj.com/content/361/bmj.k2396
https://www.nature.com/articles/s41467-023-42523-9
Links to Cancer and Mental Health
The eating habits we have are going to affect how likely we are to get some form of cancer; ultra-processed foods may be associated with an additional 12 percent in overall incidence of all forms of cancer. Some diets that are good for us (such as the Mediterranean diet) can reduce the risk of getting breast cancer by as much as 25 percent due to the antioxidants and anti-inflammatory agents contained within them. Cohort studies show that there is an 8-11 percent decrease in the risk of developing colorectal cancer when individuals consume high amounts of dietary fiber and low levels of red meat. The Alternate Mediterranean Diet is negatively related to the development of lung and oesophageal cancers.
https://www.bmj.com/content/384/bmj-2023-077310
https://www.nature.com/articles/s41467-023-42523-9
Mental health also benefits from nutritious diets. Convincing evidence ties ultra-processed foods to higher anxiety (48% odds) and depression risks. Ketogenic diets aid in managing epilepsy and neurological conditions, while plant-based patterns reduce depression and dementia incidence. The Mediterranean diet supports cognitive health, potentially lowering Alzheimer’s risk through phenolic compounds.
https://www.bmj.com/content/384/bmj-2023-077310
https://pmc.ncbi.nlm.nih.gov/articles/PMC9921002
Diet and Autoimmune Diseases
The food we eat can have an impact on the development and severity of auto-immune diseases such as rheumatoid arthritis (RA), multiple sclerosis (MS), and Hashimoto’s thyroiditis (HAT). Diets that promote systemic inflammation, due to excessive sugar, salt, and processing, may increase the likelihood of developing an auto-immune disease or worsen existing symptoms such as those found in MS. On the other hand, there is evidence that anti-inflammatory eating patterns, such as the Mediterranean Diet (MD), may help reduce the risk of developing an auto-immune disease. For example, studies have shown that individuals who adhere to the MD at a higher rate than others may experience lower levels of inflammatory markers associated with RA and lower risk of developing RA over a 9-year period. Similarly, studies have found that Hashimoto’s Thyroiditis (HAT) patients who consumed poor quality diets were more likely to be overweight, experience fatigue, develop depression and experience a poorer quality of life compared to their counterparts. The MD has been shown to provide protective effects against HAT by decreasing oxidative stress through its content of omega-3 fatty acids, polyphenols and selenium. Another important aspect of auto-immune diseases is the relationship between the gut microbiota and the presence of dysbiosis. Research has shown that consuming a plant-based diet and supplementing with probiotics can improve clinical outcomes for individuals with diseases such as systemic lupus erythematosus. Therefore, lifestyle modification, specifically making healthy choices regarding our diets, will undoubtedly affect the progression of our auto-immune diseases by decreasing inflammation and enhancing our ability to fight off infection and maintain health.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12252151
https://www.sciencedirect.com/science/article/pii/S2405457724001153
https://www.nature.com/articles/s41430-025-01628-8
Diet, Immune System, and Infectious Diseases
Dietary factors can either promote or inhibit immune response. An individual with a diet that is lacking in nutrients may be at an increased risk of developing infection due to impaired immune barrier function. Conversely, an individual who consumes a well-balanced diet will be able to better protect against infection by utilizing enhanced resistance mechanisms. Vitamins (A, C, D), zinc, selenium, and omega-3 polyunsaturated fatty acids are examples of nutritional components that modulate cytokine production, help support the function of B/T cells and increase the activity of antimicrobial compounds, for example, vitamin D has been shown to reduce the frequency of respiratory infections. Omega-3 polyunsaturated fatty acids have anti-inflammatory properties and amino acids such as arginine have been found to stimulate the function of macrophages. In addition, a poor diet that includes inadequate amounts of necessary nutrients is also associated with alterations in the composition of the intestinal microflora which will subsequently increase an individual’s risk of developing infections. Finally, research indicates that individuals consuming a well-balanced diet rich in necessary nutrients will exhibit reduced risks of developing infections.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9772031
https://pmc.ncbi.nlm.nih.gov/articles/PMC7967579
Diet and Respiratory Diseases
Pro-inflammatory dietary habits (i.e., high amounts of added sugars, sodium, and nitrites) are associated with an increased risk for Asthma-COPD Overlap Syndrome (ACOS). Higher intakes of fiber have been shown to reduce the prevalence of COPD; particularly in males. Individuals who adhere most closely to a “Planetary Health Diet Index” (PHDI), i.e., those individuals who consume the least number of processed foods, meat, dairy products, and refined carbohydrates, experience a 27% reduction in their likelihood of developing COPD compared to the lowest tertile of PHDI scores; this is likely due to decreased levels of systemic inflammation. Prudent eating patterns that are characterized by high consumption of fruits, vegetables and fish appear to be protective against the development of COPD, as these dietary patterns are associated with a reduced risk of developing COPD. Conversely, Western-type dietary patterns that include high intakes of processed foods and low intakes of fruits, vegetables and whole grains are associated with an increased risk of developing COPD. Overall, healthy dietary patterns that include fruits, vegetables, and whole grains may decrease the incidence of COPD, which likely results from the anti-inflammatory and antioxidant effects of these food components.
https://www.nature.com/articles/s41598-024-58813-1
https://bmcpulmmed.biomedcentral.com/articles/10.1186/s12890-025-03501-7
https://www.sciencedirect.com/science/article/abs/pii/S0954611125000757
Diet and Bone Health: Preventing Osteoporosis
Consumption of healthy diets is associated with increased bone mineral density (BMD), as well as decreased incidence of fractures. Conversely, Western diets that include a high intake of processed foods, sweets etc., are associated with decreased bone mineral density and an increased incidence of fractures. The association between a diet that follows a Mediterranean pattern and bone health has been shown to be positive; individuals who follow this type of diet have significantly greater bone mineral density than non-adherents and have a lower incidence of hip fractures. Calcium, vitamin D, potassium, and magnesium provide components for bone formation as well as help to neutralize acids in the urine which can otherwise cause the body to lose bone mass. There does not appear to be any adverse effect of consuming large amounts of protein if sufficient calcium is consumed. Consuming less salt, saturated fat, and processed meats will also aid in preserving bone mass.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5227978
Diet and Skin Health
The diet impacts skin diseases such as acne, eczema, and psoriasis through both the gut-skin axis and inflammation. For example, foods that are high glycemic and have an abundance of dairy products and/or omega-6 fatty acids will likely make acne worse. Conversely, low glycemic diets rich in omega-3 fatty acids and containing probiotic supplements can help reduce symptoms of acne. Regarding eczema, by eliminating known allergens (such as milk, egg), adding omega-3/6 fatty acid supplements and vitamin supplements along with probiotics to their regimen is beneficial; it has also been noted that mothers who breastfeed while limiting their exposure to potential allergens may be able to provide a protective effect to their infants. For individuals with psoriasis, there is evidence that reducing caloric intake and eating a diet that is either Mediterranean, gluten-free, or a combination of these dietary options can be beneficial for those with psoriasis. Therefore, it would be advisable for individuals with psoriasis to limit their consumption of gluten-containing foods, sugars, red meat; whereas including omega-3 fatty acids, vitamins D and B12 into their diet may help manage this disease. The relationship between gut dysbiosis and the flare-ups associated with all three skin diseases emphasizes the importance of consuming adequate amounts of fiber and prebiotic rich foods.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10982215
https://www.aad.org/public/diseases/acne/causes/diet
https://pmc.ncbi.nlm.nih.gov/articles/PMC7916842
Conclusion
Diet has a strong impact on health; unhealthy dietary habits are associated with increased risk for a multitude of chronic disease states, while healthy dietary habits provide significant protective effects in all body systems. Healthy dietary habits include consuming whole foods, anti-inflammatory nutrients, and evidence based diets such as the Mediterranean diet and plant-based diet. These practices will help to reduce risk factors, decrease symptoms, and increase longevity. Making healthy dietary habits available to everyone is dependent upon public health initiatives, such as government policy that limits access to highly processed foods and promotes nutrition education.
