For over thirty years, the Mayo Clinic has been combating the rumor that they recommend a version of a quick weight loss diet that touts the consumption of grapefruit, vegetables, fruits and unlimited portions of meat and fat. The clinic has repeatedly issued statements that the so-called ‘Mayo Clinic Diet’ did not originate at the Mayo Clinic and is not endorsed by them. In fact, they have gone so far as to state that it may be unhealthy for some people.
A visit to the Mayo Clinic web site will take you to the REAL Mayo Clinic diet, and their recommendations and guidance for weight loss that is healthy and permanent.
Summary:

Weight loss results from expending more calories than you consume. The only way to lose weight is to eat fewer calories than you use in your daily activities. The only way to achieve permanent weight loss is by adopting a balanced, healthy diet with portions that fit your lifestyle, and engage in regular physical activity.

The healthiest, most beneficial diet for you is one that takes your individuality into account. There is no ‘one perfect eating plan’ - not even one that will work for you ‘for the rest of your life’. Your body needs different things at different stages. Illnesses and allergies, high stress periods - all result in changing nutritional needs for your body.
Basic Recommendations: The Seven Basic Rules

1. Eat more fruit and vegetables.
2. Reduce intake of saturated fats and cholesterol
3. Cut back on sweets and salt
4. Drink alcohol in moderation, if you must drink at all
5. Learn to eat moderate portions of food
6. Control the number of calories you consume
7. Include physical activity in your daily activities
Specifics by Food Group

Carbohydrates

Carbs are the body’s main energy source. Complex carbohydrates such as whole grains, legumes and dried beans and grains are a staple of the Mediterranean diet, where heart disease, diabetes and obesity are extremely low.

Recommendation: 45 to 65% of your daily calories should be from carbohydrates. Focus on the complex carbohydrates, milk and fruit, and keep your intake of sugar, white flour and candy low.
Cholesterol

Your body uses cholesterol to build and help cells function properly. Typically, our bodies make all the cholesterol needed, and additional cholesterol is deposited on the sides of arteries and organs. Cholesterol is found in meat, poultry, eggs, dairy products and seafood.

Recommendations:

Limit intake of cholesterol to no more than 300 milligrams daily
Fat

One of the most concentrated sources of energy-fat-has more calories than protein or carbohydrates. Your body needs it to absorb some vitamins and build healthy cells and neural pathways. The kind of fat is important, though. Trans and saturated fats (from red meats, among other things), can raise your cholesterol level and heighten your risk of heart attacks.

Recommendation:

Aim for 20 to 35% of daily calories from fat. Focus on vegetable oils, nuts and fish oils rather than most animal sources.
Fiber

Fiber is the bulky part of vegetables. There are two types of fiber - soluble and insoluble. Your body needs both. Fiber is derived from bran, oats, wheat, green vegetables, apples and other fruits.

Recommendations:

For women: 21 - 25 grams fiber daily
For men: 30 - 38 grams fiber daily

As you can see, the real Mayo Clinic diet emphasizes a balanced diet derived largely from complex carbohydrates, fresh vegetables, little meat, and careful choice of fat. They advocate slow, steady weight loss rather than quick, take-it-off-now methods, and strongly suggest that the best eating plans are those that can become the basis for a lifelong change in eating habits. Along with those general recommendations, the clinic’s Nutrition Center makes specific recommendations for each food group. Specifically:
Protein:

Protein is an essential nutrient for nearly every system in the body. It’s contained in your skin, bones, muscles, blood, organs, hormones and enzymes. The major sources of dietary protein are meat, seafood, poultry, legumes, seeds and nuts.
Recommendations:

Between 10 and 35% of your daily caloric intake should be from protein-rich sources.
An Interesting Exercise

One of the contentions of the Mayo Clinic is that one-size fits all diets won’t work for everyone. One of the most helpful parts of their Nutrition Center is their Daily Calorie Calculator. A link on the home page will take you to a Healthy Diet Calculator that will help you calculate a personalized eating plan to help you lose weight.

Here’s an example of what your personalized plan could look like:
Subject: Female, 225 lbs, 5 ft 6”
Recommendations:

Daily calorie goal for weight loss: 1200 calories
Sweets and extras: up to 75 calories daily
Fats: 3 servings
Protein/Dairy: 3 servings
Carbohydrates: 4 servings
Fruits: 3 or more servings
Vegetables: 4 or more servings
Further links offer a sample menu at that calorie level, and specific recommendations that will help you lose weight. Those tips include:
Increase the ratio of fruits and vegetables in meals
Experiment with new foods and combinations.
Start with a soup or salad.
Learn healthy cooking techniques.
Consider energy density of food.
Energy density?

The Mayo Clinic defines energy density as the number of calories in food vs. the amount of food. A sugary dessert may have extremely high energy density - in other words, a small serving provides a lot of calories. Consequently, it takes far more of that food to make your body feel full. Foods like broccoli have a much less energy density - 15 calories in a regular portion. You eat far less of it and feel full more quickly.
The basic recommendations made by the Mayo Clinic aren’t ground-breaking. They advocate sensible eating, low calories and increasing your physical activity. The suggestion to aim for 1-2 pounds lost per week is echoed by nearly every other medically noteworthy institute in the country. It’s a real diet - the real Mayo Clinic Diet.