With so many different diets available, deciding what to eat can seem overwhelming. This two part video series will attempt to answer the question: what diet is best for health? Part 1 of this video series will review different diets along with their rationale. Part 2 will look at research to discuss which diet is best, if any, with a particular emphasis on diets for weight loss. According to Merriam-Webster Dictionary, diet can be defined in several ways: The first is, food and drink regularly provided or consumed. In this sense, diet is just the regular way that people eat and drink. For example, the “mediterranean diet” is adopted from the eating habits of people who live in countries that border the Mediterranean Sea, such as Italy and Spain for instance. 2. The kind and amount of food prescribed for a specific reason. For example, patients with celiac disease will be prescribed a gluten-free diet from their doctors 3. A regimen of eating and drinking sparingly to lose weight. The last definition is perhaps the most common one that we associate with. Let’s review the defining characteristics of many common diets along with their rationale next. First we have what’s called a mixed-balanced diet. A mixed, balanced diet can be considered as one that includes both plant and animal foods and follows the Dietary Reference Intake (DRI) recommendations. These guidelines represent the most current scientific knowledge on nutrient needs for healthy populations. These guidelines suggest that between 45 to 65% of your calories are coming from carbohydrates, between 10 and 35% of your calories coming from protein, and between 20 and 35% of your calories coming from dietary fat. The focus of a mixed, balanced diet is to not restrict any one type of food. It allows for flexibility and recommends avoiding processed junk foods, which are typically high in calories, sugar, fat, and salt, and low in fibre as well as nutrients. Next, we have low-fat diets. A low-fat diet is one that reduces the consumption of dietary fat. As a result, this diet increases the consumption of protein and/or carbohydrates. There is no official definition of what constitutes a low-fat diet. According to the DRI recommendations that we saw earlier, any diet that has a fat intake below 20% of total daily calories can be considered a low-fat diet. Low-fat diets have been popular since the early 1900’s. Since dietary fats have 9 calories per gram, whereas both proteins and carbohydrates have 4 calories per gram, cutting fat seemed like a logical way to cut calories and therefore lose weight. Low-fat diets were soon recommended for everyone because of the “diet-heart hypothesis”. In the early 1960’s, epidemiological studies showed a correlation between consumption of dietary fat, specifically animal fat, and death from coronary heart disease disease. This led to the recommendation that low-fat diets will lower the risk of coronary heart disease. Thus, in the late 1900’s, low fat-diets were soon recommended and promoted by doctors, the government, and the media as not only a way to lose weight, but a preventative measure for all. Next, we have low-carbohydrate diets. A low-carbohydrate diet is one that reduces the consumption of carbohydrates. As a result, this diet increases the consumption of protein and/or dietary fat. There is no official definition of what constitutes a low-carbohydrate diet. The Institute of Medicine recommends that adults get 45% – 65% of their daily calories from carbohydrates. Thus, according to these guidelines, any diet that has a carbohydrate intake below 45% of total daily energy intake can be considered a low-carbohydrate diet. Recently, low-carbohydrate diets have become quite popular. The rationale for low-carbohydrate diets is the “carbohydrate-insulin hypothesis”. The idea here is that carbohydrates (especially heavily processed ones) increase levels of insulin in the bloodstream, which eventually causes our bodies to store fat. Advocates of this model believe that weight gain is caused by elevated insulin levels and not excess carbohydrate consumption. Next, we have the ketogenic diet. The ketogenic diet can be thought of as an extreme version of a low-carbohydrate diet. Ketogenic diets have become popular recently as a way to lose weight. In the 19th century, the ketogenic diet was commonly used in patients to help control their diabetes. In 1920, it was used as an effective treatment for children with epilepsy whom were not responding well to medication. The human body primarily relies on glucose as its main source of energy for all cells. This is especially true for the brain. When very few carbohydrates are eaten, blood glucose levels will drop. The human body can then break down stored glycogen in the liver to release glucose in the bloodstream. After a few days of this however, glucose is fully depleted, insulin levels decrease, and the body can then begin using fat as its primary source of energy in place of glucose. When body fat is broken down, compounds called ketone bodies are produced, which can be used as an energy source when glucose is unavailable. As the concentration of ketone bodies in the blood rises, we enter a state called ketosis. Any diet that puts the body into a state of ketosis is called a ketogenic diet. There isn’t one standard ketogenic diet, but they typically have between 70 – 80% of Calories coming from dietary fat, 10 to 20% of Calories coming from protein, and 5 to 10% of Calories coming from carbohydrates. Ketogenic diets can be very restrictive. They allow foods high in saturated fat such as fatty cuts of meat, lard and butter as well as sources of unsaturated fats such as plant oils, nuts and seeds, and avocados. They allow very small amounts of non-starchy vegetables such as peppers, zucchini, and broccoli just to name a few. Ketogenic diets ban carb-rich foods such as grains, starchy vegetables, legumes, and most fruits. The rationale for ketogenic diets is that they may be useful as a short term treatment for people with metabolic diseases such as type 2 diabetes. More recently however, ketogenic diets have become popular as an easy way to lose weight. Next, we have the Mediterranean Diet. Mediterranean diets are based on the eating habits of people who live in countries that border the Mediterranean Sea. These diets vary but typically emphasize consumption of olive oil, fruits and vegetables, beans, legumes, nuts and seeds, whole grains, and seafood. The rationale for Mediterranean eating is that it has been associated with: increased longevity, healthy aging, and reduced risk of cardiovascular disease. Next, we have the paleolithic diet. The paleolithic, paleo, or primal diet is based on the premise that we should eat the same way that our stone age ancestors did. This involves eating a diet rich in fruits, vegetables, nuts and seeds, eggs, and lean meats. The Paleo diet avoids eating processed foods, dairy, and grains. The rationale for the Paleo diet is based on the principles that we are adapted to eat certain types of foods. The belief is that the change from a hunting and gathering diet that was rich in fruits and vegetables to an agricultural diet that is rich in grains has led us to develop many chronic diseases such as obesity, diabetes, and cardiovascular disease. Thus, in order to avoid these diseases and live to be fit and strong, we need to eat like our ancestors. Up next, we have vegetarian diets. Vegetarians diets are mostly plant-based and generally exclude the consumption of meat. Vegetarian diets vary. Some may include eggs and dairy as well as certain animal products such as fish and seafood. People choose to eat vegetarian for a variety of reasons, such as: concern for animal life, personal health, and cultural reasons. Next, we have vegan diets. A vegan diet can be thought of as an extension of vegetarianism. It is one that excludes all animals products such as meat, poultry, seafood, eggs, and dairy. Vegan diets emphasize eating whole, plant-based foods. Such diets are high in fibre and nutrients, and low in dietary fat. People choose to go on a vegan diet for a variety of reasons, such as: concerns about the treatment of animals, concerns about the impact of animal agriculture on the environment, and personal health. There are of course many other dietary patterns as well. Some of these include: intermittent fasting, raw-food eating, and juicing, just to name a few. These diets will not be discussed further here, but may be the topic of a future video. This conclude part 1, in which a variety of dietary patterns, along with their rationale were discussed. In part 2 of this video, we will discuss which diet is best for health, if any exist at all, with an emphasis on diets for weight loss. Have a question? Leave it in the comments below! If you liked this video, be sure to give it a like, and subscribe to this channel for more!