While many people continually “go on a diet” (and then another and another), everyone has a diet. I’ve never gone on a diet, but I’ve always had a diet. As I always say, diet should be viewed as a noun, not a verb. It’s a thing you have, not an action you take. Every action has a reaction (intended or otherwise), so any diet plan you initiate can quickly be halted in favor of something else.
If you instead think of your diet as part of your lifestyle, you’re much more likely to stick to it. 
Everyone has a diet, but not everyone gets good nutrition. In the minds of many people, low-calorie means healthy. Yet, this isn’t necessarily true.
For example, a rice cake has just 35 calories. Yet, it is almost entirely devoid of fiber and protein. Though a rice cake has very few calories, it also has very little nutrition, not to mention that it’s entirely processed.
On the other hand, an avocado, which grows on a tree, is both calorically and nutritionally dense. An avocado can weigh anywhere from 8 ounces to 3 pounds (48 ounces). So, serving size matters.
One cup (8oz) of sliced avocado has 234 calories and 21 grams of fat, most of which is monounsaturated. It is packed with fiber (10g) and potassium (more than a banana), and is also a great source of vitamin-C, folate and B-6. Additionally, it has virtually no sugar (despite being a fruit) and very few carbs (for those who care about such things).
In short, an avocado is loaded with healthy fats, fiber and various important nutrients.
Yet, some people would choose a nutritionally lacking rice cake over an avocado simply because it is lower in calories. Bad move. Caloric content and nutritional content are not necessarily related. 
No one thinks of a Big Mac as health food. Yet, you could eat three Big Macs a day and still lose weight. Don’t believe me? Well, a Big Mac has just 550 calories. Eat three a day and you’d ingest just 1,650 calories. Since the average American now eats a whopping 3,660 calories per day, eating one Big Mac for breakfast, lunch and dinner would cut that average intake by more than half. Do that, and watch the pounds melt away!
However, you’d be missing lots of important nutrition on the Big Mac Diet. McDonald’s signature sandwich has minimal calcium, potassium and fiber, and zero vitamin D. However, it is loaded with sodium (44% of the daily value) and has 11 grams of saturated fat (53% of the daily value). Eat three a day and you’d be ingesting an enormous amount of salt and unhealthy fat.
Oh, and one Big Mac also has nine grams of sugar. Eat three of them and you’d intake 27 grams of sugar, which is above the 24-gram daily limit recommended for women by the American Heart Association.
Yet, on this Big Mac Diet you’d lose weight, and that would ultimately have a positive effect on your health. Scientific evidence shows that losing just 10 pounds can decrease hypertension, improve good cholesterol (HDL), lower triglycerides, decrease insulin resistance, reduce inflammation in blood vessels, improve or reverse sleep apnea, and increase energy and vitality.
That said, there are better, healthier ways to lose weight than the Big Mac Diet. 
The point is that calories and nutrition are not synonymous. You can eat a low-calorie diet that is not healthy. More to the point, you can eat a low-calorie diet and not necessarily be healthy.
On the other hand, you can eat a very healthy diet featuring high-calorie foods that are packed with nutrition (i.e., avocados, nuts, nut-butters, salmon, whole-fat yogurt, etc.). Additionally, high-calorie foods are more filling than most low-calorie foods (like rice cakes), meaning you might ultimately eat less.
Low calorie foods are not necessarily nutritious, beneficial or preferable. And high-calorie foods are not necessarily unhealthy or to be avoided. The goal should be to maximize nutrition at each and every meal, even if you also seek to limit calories.
If you need to lose weight to be more healthy, you can do this by eating healthy, whole foods, such as fruits, vegetables, a wide variety of animal- and/or plant-based proteins, plus whole grains (There’s more than just wheat, people! Try spelt, millet, amaranth, quinoa, black or red rice, whole oats, etc.).
And, yes, you can indeed lose weight by including healthy, high-calorie foods in your diet. You just need to limit your total caloric intake. To do that, you need to track your daily caloric input. And you should also know how many calories you need each day.
As the Twinkie Diet proved, you can eat an unhealthy diet and still lose weight. The Big Mac Diet would be no different.
By the same token, you can have a healthy diet and still gain weight, if your caloric intake is higher than your needs.
To lose weight, it comes down to quality and quantity. You should aim for higher quality foods, and a lower quantity of them, each day.