As some may know, I am a certified personal trainer and exercise science major. One of the most misunderstood concepts to fitness that I address with people is that about dieting. Everyone has someone they know that did diet A, B, or C and had "Success"! This makes battling misinformation extremely difficult, even when you're educated and trained specifically in the topic!
So what is the big secret to a successful diet?
The most underlying concept and basis of EVERY. SINGLE. DIET. is that you MUST achieve a caloric deficit. What does that mean? It means that the amount of energy you intake HAS to be less than the amount of energy you expend! If that doesn't happen, it does NOT matter what diet you are doing! Be it Keto, paleo, low carb, low fat, the ridiculous "water" diet, etc. Every single one is trying to help you accomplish one thing and one thing only. To reduce the amount of calories you intake.
Now according to todays scientific understanding, any diet that restricts any single macro nutrient (protein, carbohydrates, fats) should definitely be taken with suspicion. Understanding how the body functions and its energy systems is important to understanding why carbs, fats, and proteins are essential in MOST peoples diets! Before you ever engage in any of these diets, I would highly recommend you speak with a dietitian first! Restricting any single macro nutrient can be detrimental to your health, especially if done incorrectly. It can also reduce your energy levels depending on the situation.
For example, the Keto diet restricts your intake of carbohydrates, the bodies primary fuel source for moderate to heavy exercise. It is also the fuel source for your brain, a key reason on why you have to ingest at least 50g of carbs a day even when on the diet. The brain cant function without it. This is why hypoglycemia (low blood sugar levels) causes deliriousness, foggy mind, memory problems, and even death!
So what is the best "diet"?
Lets define this word that has become synonymous with "reduced calories". Diet just means the composition of your intake. Thats it. Diet does not necessarily mean caloric restriction. For example, bodybuilders change their diet to an increase in caloric intake so that they can put on muscle tissue.
So to answer the question. The best diet is a balanced one. One that has carbs, fats, and protein! These should be healthful options as well! Whole grains, healthy fats (such as avacado, olive oil), and quality protein. Too often I see people eating "keto" and its greasy, saturated, unhealthy fats! That diet isn't an excuse to eat like shit.
Often I hear, "I dont want to count calories". However, if you do any of these diets such as Keto, YOU STILL HAVE TO COUNT MACROS! This is essentially the same thing as counting calories! Macronutrients are caloric related! If you are counting macros, you are counting calories!
The problem with the mainstream misinformation is that people want "the magic pill" that just fixes your health. It does not exist. To take control of your health you have to take control of your diet and your exercise. Both are important! The body is meant to move! So eat a balanced diet, with healthier options, count those macros (but all of them) and make sure you use your diet to optimize your energy while providing the nutrition you need, even while trying to "lose weight".