Most people's daily caloric requirement is 2000 to 2500 cal. As a rule of thumb, patients can roughly calculate the number of daily calories they require by multiplying their current weight in pounds by 13 (or 15 if they are active). Those patients with a body mass index (BMI) of 27 to 35 should reduce their total calories by 300 to 500 daily, and those with a BMI greater than 35 should reduce their total calories by 500 to 1000 daily. These reductions will produce the recommended weight loss of 1 to 2 lb per week in most patients (see http://nhlbisupport.com/bmi/bmicalc.htm for information on calculating BMI).

TABLE 2. Recommended average daily energy allowances

Physicians should counsel patients that they need to pay attention to the number of calories listed on food labels. Within the last 2 decades, calories per portion have increased dramatically.⁴ For instance, a can of soda 20 years ago had 85 cal; today it has approximately 250 cal. An order of French fries used to contain 210 cal; now a regular order exceeds 600 (see Table 2). The average American consumes 500 more calories per day now than they did in 1970.

Carbohydrates The Krebs cycle converts carbohydrates into glucose, and then insulin is released from the pancreas to facilitate conversion and storage of the glucose as fat. The insulin release suppresses fat utilization. As a result, consumption of too many carbohydrates can lead to weight gain. In evaluating carbohydrates in the diet, it is important to keep in mind that carbohydrates can be either simple or complex.

Simple carbohydrates include fructose, sucrose, and lactose. These sugars occur naturally in fruits, milk products, and vegetables. However, they are also found in processed and refined sugars such as candy and nondiet carbonated beverages and have little nutritional value.

Complex carbohydrates are also made up of sugars, but the sugar molecules are strung together to form longer, more complex chains. They consist of at least 3 sugars. Foods rich in complex carbohydrates include starchy vegetables, pastas, and whole grains. They are a good source of vitamins, minerals, and fiber.

When consuming carbohydrates, patients should try to select unrefined foods such as fruits, vegetables, and whole-grain products instead of refined, processed foods. For most people, fewer than half of their total calories should come from carbohydrates, and those should be complex in nature.

Fats Approximately 20% to 30% of calories should come from fat (see "IOM recommended dietary reference values"). Patients can determine the ideal total daily number of fat grams by multiplying their daily caloric intake—typically 2000 to 2500 cal—by 20% to 30% and then dividing the result by 9. Typically, this ranges from 50 to 90 g. Emphasize that no more than 10% of calories should come from saturated and trans fat.

There are 3 types of fat—monounsaturated, polyunsaturated, and saturated—and patients should understand the difference because some fat is essential. For example, the absorption of vitamins A, D, E, and K is dependent on fat. The key is to consume healthy fats.

Mono- and polyunsaturated fats include fats not produced by the body. Therefore they must either be consumed as part of the diet or augmented by supplements. Omega-6 fatty acids (linoleic acids) and omega-3 fatty acids (alpha-linolenic acids) are unsaturated fats. The omega-6 fatty acids are fairly plentiful in food—cereals, whole-grain breads, soybeans, and vegetable oils, including safflower, sesame, sunflower, olive, and corn oils. Daily omega-6 consumption should be 17 g for men, 12 g for women.

Because omega-3 fatty acids are limited in the food supply, many diets are deficient in them. The richest sources of omega-3 are flaxseed oil, pumpkin seeds, fish oil, and some types of nut. Within the last few years, there have been numerous studies published regarding the health benefits of omega-3 fatty acids, which can reduce triglyceride levels, lower BP, prevent arrhythmias, reduce cardiac events, improve mood, decrease inflammation, and may even reduce the risk of certain malignancies, such as prostate cancer. They also appear to affect satiety by slowing digestion and stabilizing blood glucose levels.

Omega-3 fatty acids are broken down into 2 other fats—EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)—found predominantly in fish and fish oils, specifically cold-water fish like salmon, halibut, herring, mackerel, sardines, and albacore tuna. They are also found in walnuts, soybeans, and canola oil.

One should recommend a daily omega-3 goal of 1.6 g for men and 1.1 g for women. This translates into 2 servings of fish a week. One can also use supplements such as fish oil capsules, which are high in EPA and DHA.

Trans fats are created from polyunsaturated fats during the partial hydrogenation process that converts liquid oil into solid fats. Hydrogenation is performed to permit longer shelf life, but omega-3 fatty acids are destroyed during partial hydrogenation.

Saturated fats have the maximum possible number of hydrogen atoms attached to every carbon atom. Linked to increased LDL levels, saturated fat is found in animal products and coconut and palm oil.

POPULAR DIETS Because nearly a third of patients are on diets, a review of today's most popular ones may be helpful when giving nutritional advice. A recent systematic review of the major commercial weight-loss programs concluded that with the exception of Weight Watchers, evidence to support recommending those diet programs was found to be suboptimal.⁸ Adherence is generally an issue, and weight gain after abandoning a regimen is the norm.

Low-calorie commercial diets Weight Watchers, Jenny Craig, LA Weight Loss, Medifast, and eDiets are among patients' options for a low-calorie diet plan. A recent study showed that persons who regularly attended Weight Watchers, which features an exchange diet, lost approximately 5% of their initial weight over a 3- to 6-month period.⁵ The Jenny Craig diet plan features prepackaged meals, and Medifast's diet is provided through meal replacement. Most others involve patients preparing their own meals. Good results reported by those plans generally do not take into account the significant percentage of patients who did not complete the regimens.

Low-carbohydrate plans Low-carbohydrate diets have become popular within the last few years, notably Atkins and South Beach. Typically, these diets exclude vegetables, fruits, whole grains, and beans. This raises some concern because these foods have been linked to reduced risk of some cancer, heart disease, and stroke.

The Atkins diet is high in fat (55%-65% of total calories) and low in carbohydrates (less than 100 g/d). The first 2 weeks is termed the "induction" period, during which dieters are permitted no more than 20 g/d of carbohydrates. The result is a steady intake of protein-rich, high-fat foods such as steak, poultry, seafood, eggs, cheeses, oils, butter, margarine, bacon, and sausages. The 20-g carbohydrate limit generally comes from trace amounts of carbohydrates found in sauces, dressings, cheeses, and vegetables. During the 2-week period, participants are allowed to have little, if any, milk, fruits, grains, cereals, breads, or high-glycemic-index vegetables such as potatoes, corn, and carrots.

After the first 2 weeks, dieters can begin adding about 5 more g of carbohydrates a day to their diet weekly. Generally, a diet consisting of no more than 40 to 90 g/d of carbohydrates is suggested as a maintenance phase.

The South Beach diet is a high-protein, low-fat, low-carbohydrate plan that focuses on low-glycemic-index foods. Low-glycemic-index foods cause a low rise in blood glucose, with a subsequent small increase in insulin, which ultimately may promote satiety and less fat deposition.

The diet has 3 phases: initial rapid weight loss, gradual weight loss, and maintenance. In contrast to the Atkins diet, the South Beach Diet does not severely limit carbohydrate intake nor does it promote fat intake. Rather, it focuses on "good carbs," such as fruits, vegetables, and whole grains, and "good fats," unsaturated fats that have a low glycemic index.

Low-fat plans The Ornish diet is based on a food intake that is 10% fat, 20% protein, and 70% carbohydrates. The few plant-based foods that are high in fat are excluded, including all oils (other than 3 g/d of flaxseed oil or fish oil to provide additional omega-3 fatty acids), nuts, and avocados. The diet consists primarily of fruits, vegetables, grains, and beans, including soy-based foods, supplemented by moderate amounts of nonfat dairy and egg whites. There is no caloric restriction so long as the diet is confined within the recommended foods. The Ornish diet actually consists of 2 diets.

The "reversal diet" is designed for patients who have been diagnosed with heart disease or high cholesterol levels. Although originator Dean Ornish, MD, has published several studies demonstrating reversal of heart disease for a select group of patients undergoing his program, he states that his diet alone is not sufficient for reversing heart disease but is only 1 part of an overall program that includes exercise, yoga, meditation, stress reduction, and lifestyle changes. The whole-foods vegetarian diet is high in complex carbohydrates, low in simple carbohydrates, and very low in fat—approximately 10% of calories.

The "prevention diet" is designed for patients who do not have heart disease but whose total cholesterol level is above 150 mg/dL. The diet is also meant for people with a ratio of total cholesterol to HDL that is less than 3.0.

RESEARCH FINDINGS Several studies have recently been published comparing low-carbohydrate and low-fat diets for weight loss. In one, 132 patients with a BMI greater than 35 were randomized to either a low-carbohydrate diet—less than 30 g/d—or a low-fat diet—less than 30% calories from fat.⁶ Although the low-carbohydrate group lost more fat at 6 months, both groups had the same weight loss at 1 year (6-10 lb). Of note, there was no difference between groups in total and LDL cholesterol levels. Both groups had a dropout rate of nearly one third.

Another study randomized 120 patients to either a low-carbohydrate or low-fat diet.⁷ Subjects had a BMI greater than 34, and all were hyperlipidemic. The low-carbohydrate diet initially allowed less than 20 g/d and then added 5 g/d later in the course. The low-fat diet allowed less than 30% calories from fat. At 6 months, the average weight loss was 12 kg in the low-carbohydrate group and 6.5 kg in the low-fat group. Although the mean LDL level was similar between groups, total and HDL cholesterol levels improved in the low-carbohydrate group compared with the low-fat group.

In a systematic review of major commercial weight loss programs including Weight Watchers, Optifast, ediets.com, Overeaters Anonymous, and Jenny Craig, researchers found that there are few high-quality studies to determine the effectiveness of these programs.⁸ Most data are anecdotal in nature. However, the authors found that of all the programs looked at, Weight Watchers had the strongest studies to support its claims, with participants on average losing 5% of their initial body weight at 6 months, and 3% at 2 years.

A study comparing the Atkins, Ornish, Weight Watchers, and Zone diets for their effect on weight loss and heart disease risk reduction involved 160 patients ranging in age from 22 to 72 years.^9,10 All had at least 1 risk factor for heart disease, such as hypertension, dyslipidemia, or fasting hyperglycemia, and most were obese. Patients were randomized to 1 of the 4 diets, received counseling on their plans for 2 months, and then had to follow the diet on their own for 10 months.

At the end of 1 year, all the patients lost weight—approximately 4%. The Ornish diet demonstrated a 6.2% weight loss. In addition, all groups showed both a reduction in LDL cholesterol and an increase in HDL cholesterol levels. Moreover, all patients who completed the study showed some reduction in risk of heart disease at 1 year irrespective of diet. However, by 1 year, approximately half of the patients enrolled in the Atkins and Ornish programs had dropped out, and a third of patients in the Weight Watchers and Zone program had quit. This creates a potential "yo-yo" effect, resulting in a cycling pattern of weight loss and gain.

A SOUND NUTRITIONAL PLAN Patients should understand that it is not the particular diet that is important, but rather the need to follow a sound nutritional plan that results in weight loss over time.

Help patients keep nutritional strategies simple. Most understand the concept that they need to eat food from all food groups. The key is moderation. Small, stepwise changes can have a big impact. For instance, reducing intake by as little as 100 cal/d translates into 10 lb of weight loss in a year.

This simple but effective advice is based on the recent Dietary Guidelines for Americans 2005 published by the Department of Health and Human Services and the Department of Agriculture:

• Eat at least 5 servings a day of vegetables and 4 servings of fruits
• Eat few simple carbohydrates, such as sugar, white flour, and white rice
• Focus on complex carbohydrates, such as unrefined whole-wheat bread, brown rice, and beans
• Choose whole grains over processed cereals; eat 6 oz per day, including 3 oz of whole grains and 3 oz of other grains
• Add fiber to your diet
• Strive for 3 daily servings of dairy
• Decrease saturated fats and trans fats by eating more fish (at least twice a week) and less red meat.¹¹