I'd like to share a huge non-secret with you: "Poor diet is a major contributor to the leading causes of chronic diseases and death in the United States, including coronary heart disease, diabetes, hyperlipidemia, and stroke". 
Although it is true that the obesity and chronic disease epidemics have complicated origins, the contribution of our modern society's easy access to highly processed foods, low consumption of fresh and whole foods, limited physical activity and busy lifestyle cannot be overemphasized.
In the recent past, numerous diets have been developed to combat weight gain and other disease risk factors, with varying degrees of evidence to show benefit. This review highlights 5 diets, each of which has a robust body of supporting literature: the Dietary Approaches to Stop Hypertension (DASH) diet, the Mediterranean diet, the Vegetarian diet, the Volumetric Diet, and the Paleo diet.
The DASH Diet
DASH has as its core the increased consumption of fresh fruits and vegetables, low-fat dairy products, nuts, legumes, whole grains, and limited intake of red meat, salt and added sugar. It is rich in potassium, magnesium and calcium, as well as protein and fiber.
Fruits and vegetables are important because of the low-caloric and high-nutrient density of such foods and the satiating effects of fiber. Fruits: up to 4-5 servings a day. Vegetables: up to 4-5 servings a day.
Low-fat dairy consumption provides protein, up to 2-3 cups of milk or 8-12 oz of yogurt a day.
Nuts and seeds are rich in beneficial mono- and polyunsaturated fats and are high in fiber and protein, 1 serving a day.
Legumes are a rich source of protein as well as fiber, 1 serving a day.
Lean meats, poultry, fish, and eggs are an important source of protein, up to 6 servings a day.
Whole grains provide an important source of energy and fiber consumption, up to 6-8 servings a day.
Salt intake is limited to 2300 milligrams per day and added sugar intake to 5 tablespoons per week for the average 2000-calories/day diet. 
DASH was originally developed and studied as a diet to reduce high blood pressure in a randomized controlled trial published in The New England Journal of Medicine in 1997. In this study, a diet rich in fruits, vegetables, and low-fat dairy products and low in saturated fat was compared with a control diet and shown to result in substantial reductions in blood pressure.
Subsequent prospective observational studies have shown the DASH diet to have a number of other beneficial health effects and lower risk of:
There are few drawbacks to the DASH diet. Some people may be troubled by the fact that it does not outline a specific way to lose weight. Other people may find it hard to adjust to eating as much fiber as the DASH diet recommends. It's a good idea to gradually add high-fiber foods, such as whole grains, fruits, and vegetables, to avoid bloating and discomfort. Portion sizes also need to be carefully monitored, and keeping to the daily sodium recommendation can be a challenge.
The Mediterranean Diet
The Mediterranean diet is a food plan that came from the olive-growing countries bordering the Mediterranean Sea (Greece, Spain, and Italy) in the 1960s. A landmark ecological study that began in the 1950s was important to the origins of this eating pattern's health benefits and showed that death rates in selected countries near the Mediterranean Sea were substantially lower compared with those in westernized countries, such as the United States and Great Britain.
In 1993, the dietary pattern was defined at the International Conference on the Diets of the Mediterranean as being characterized by:
High consumption of olive oil, legumes, unrefined grains, fruits, and vegetables
Moderate consumption of dairy products
Moderate-to-high consumption of fish
Low consumption of meat
Moderate consumption of alcohol: 1-4 drinks for men, and 1/3-2 drinks for women a day
The cardiovascular benefits of this eating plan are thought to be from its lower saturated fat content and the high content of beneficial fats, like mono-unsaturated fats, found in high levels in olive oils, and poly-unsaturated fats, found in both fatty fish and nuts.
Multiple studies in both European and US populations have shown that higher adherence to a Mediterranean food plan is associated with reduced risk for:
The Vegetarian Diet
There are different types of vegetarian diets. When people think about a vegetarian diet, they typically think about a diet that doesn't include meat, poultry or fish. But vegetarian diets vary in what foods they include and exclude:
Lacto-vegetarian diets exclude meat, fish, poultry and eggs, as well as foods that contain them. Dairy products, such as milk, cheese, yogurt and butter, are permitted.
Ovo-vegetarian diets exclude meat, poultry, seafood and dairy products, but allow eggs.
Lacto-ovo vegetarian diets exclude meat, fish and poultry, but allow dairy products and eggs.
Pescatarian diets exclude meat and poultry, dairy, and eggs, but allow fish.
Pollotarian diets exclude meat, dairy and fish, but allow poultry.
Vegan diets exclude meat, poultry, fish, eggs and dairy products — and foods that contain these products.
The vegetarian diet has been shown to reduce the risk of:
Yet some vegetarians rely too heavily on processed foods, which can be high in calories, sugar, fat and sodium. And they may not eat enough fruits, vegetables, whole grains and calcium-rich foods, thus missing out on the nutrients that these foods provide. For more information on the pros and cons of the vegetarian diet please read my blog from October 7, 2016.
The Volumetric Diet
This diet is focused on feeling full. People feel full, because of the types and amounts of food they eat -- not because of the number of calories or the grams of fat, protein, or carbs. Volumetrics relies on foods with a low-energy density and high water content, such as fruits and vegetables. Therefore, you can eat as much as you like and eliminate the feelings of hunger, fatigue, and depression that often accompany other diets.
This low-calorie, high-volume eating plan includes foods with a lot of water and fiber, since both supposedly increase your sense of fullness. It doesn’t ban any food, and you can enjoy calorie-packed foods as long as you stick within the recommended calorie intake. Foods with low energy density include:
The meals are filling and nothing is off limits. This type of dietary pattern is associated with a decreased risk of:
The Volumetrics diet plan requires a lot of home-cooked meals. Some people may be put off by the amount of time needed to cook, calculate energy densities of foods, and keep daily records. 
The Paleo Diet
This is a dietary plan based on foods similar to what might have been eaten during the Paleolithic era, which dates from approximately 2.5 million to 10,000 years ago. A paleo diet typically includes lean meats, fish, fruits, vegetables, nuts and seeds — foods that in the past could be obtained by hunting and gathering. A paleo diet limits foods that became common when farming emerged about 10,000 years ago. These foods include dairy products, legumes and grains.
The goal of a paleo diet is to return to a way of eating that's more like what early humans ate. The belief is that the human body is better suited to that type of diet than to the modern diet, which emerged with farming. Farming changed what people ate and established dairy, grains and legumes as additional staples in the human diet. This relatively late and rapid change in diet, according to the hypothesis, outpaced the body's ability to adapt. This mismatch is believed to be a contributing factor to the prevalence of obesity, diabetes, autoimmune disorders, arthritis, and heart disease today.
The paleo diet follows these guidelines:
fruits and vegetables
nuts and seeds
lean meats, especially grass-fed animals or wild game
fish, especially those rich in omega-3 fatty acids, such as salmon, mackerel and albacore tuna
oils from fruits and nuts, such as olive oil or walnut oil
Foods to avoid with a paleo diet:
grains, such as wheat, oats and barley
legumes, such as beans, lentils, peanuts and peas
potatoes and corn
processed foods in general
People don’t have to count calories or macronutrient ratios (i.e., the percentage of fat, carbohydrate, or protein they eat). Unlike the Atkins and South Beach diets, there is no need to restrict carbohydrates in order to lose weight. And unlike the Ornish and DASH diets, you can eat plenty of healthy fats that can help you stay full longer.
The paleo diet is similar to the Mediterranean diet, but eliminates legumes and grains, and some of the data showed it could be more beneficial.
The paleo diet may provide some moderate benefits when compared with diets of fruits, vegetables, lean meats, whole grains, legumes and low-fat dairy products. These moderate benefits may include:
more weight loss
improved glucose tolerance
better blood pressure control
better appetite management 
For more information on the benefits of the different diets and other health related recommendations, please schedule an appointment with Dr. Koganski at 215-750-7000 or www.newtowninternalmedicine.com.
1) Lin JS, et al. Behavioral counseling to promote physical activity and a healthful diet to prevent cardiovascular disease in adults: systematic review for the U.S. Preventive Services Task Force. Ann Intern Med. 2010;153:736-750.
2) US Department of Agriculture. Dietary Guidelines for Americans 2010. http://www.cnpp.usda.gov/dgas2010-policydocument.htm
3) Appel LJ, et al. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med. 1997;336:1117-1124.
4) Mitrou PN, et al. Mediterranean dietary pattern and prediction of all-cause mortality in a US population: results from the NIH-AARP Diet and Health Study. Arch Intern Med. 2007;167:2461-2468.
5) Foreyt, J. P. (2012). [Review of the book The ultimate Volumetrics diet: Smart, simple, science-based strategies for losing weight and keeping it off by B. Rolls & M. Herman]. American Journal of Clinical Nutrition, 96(3), 681-82. Retrieved from http://ajcn.nutrition.org/content/96/3/681.full.pdf+html
6) Lindeberg S, et al. A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease. Diabetologia. 2007 Sep;50(9):1795-807.