At any given time, over 100 million Americans are on a diet (MarketResearch .com 2014). That’s about a third of the U.S. population. Despite the hundreds of best-seller diet books and the $60-plus billion Americans spend trying to lose weight each year (Marketdata Enterprises 2014), permanent weight loss remains elusive for most. Even so, dozens of diets remain on the market, each with ardent followers and outspoken opponents.

With so many options to choose from and such avid attempts to “get it right this time,” clients may consult you for advice or directly ask what you think about a particular diet. How do you inform yourself, support your clients’ efforts and stay within scope of practice? This article reviews the pros and cons of the most popular diets, looks at pertinent research, and offers tips on how to approach this sometimes complex topic.

Diet Categories

Weight loss diets usually share at least two key features: They cut calories, and they recommend some “ideal” proportion of intake from the macronutrients (carbohydrates, protein and fat). Most diets fall into one of three categories, based on macronutrient composition: low carbohydrate, low fat and moderate macronutrient (balanced). Within each category, the diet “rules” vary considerably. Some heavily restrict certain foods, while others focus on a particular macronutrient. Others allow everything “in moderation,” while still others require specific prepackaged foods. Some— such as the DASH (Dietary Approaches to Stop Hypertension), Mediterranean, gluten-free, vegetarian and Paleo diets—are better described as “eating plans,” since they do not advocate any specific caloric restriction, but rather focus on other parameters. Like “diets,” these plans can contribute to weight loss if clients eat fewer calories overall. An overview of 20 of the most popular diets is highlighted in the sidebar “A Breakdown of Popular Diets.”

What the Evidence Says About a “Best” Diet

Advocates of various diets tend to have a physiological or nutritional explanation as to why their diet is superior. High protein intake may improve feelings of fullness and thus decrease caloric intake and enhance weight loss; low fat intake, says strong evidence, reduces the risk of a life-threatening cardiovascular event. Several studies have looked at these diets, and variations of them, in head-to-head studies comparing weight loss as well as health markers.

Two rigorous and comprehensive diet studies were published last fall. One, a meta-analysis of randomized controlled trials (RCTs) in the Journal of the American Medical Association (Johnstone et al. 2014), looked closely at weight loss. Another was a sys-tematic review of RCTs, published in Circulation: Cardiovascular Quality and Outcomes; it assessed weight loss and cardiovascular risk factors (Atallah et al. 2014).

The meta-analysis (Johnstone et al. 2014) compiled all of the RCTs to date on diets for overweight or obese individuals. The researchers then looked at weight loss 6 months and 12 months after starting the diet. On the whole, at 6 months Atkins dieters had lost the most—an average of 22 pounds. But by 12 months, weight loss across all of the diets was similar. A low-carbohydrate diet and a low-fat diet led to 13 and 15 pounds of weight loss, respectively. This was about a 7% loss of total body weight (it is well established that a 5%–10% weight loss promotes health benefits in individuals who are overweight or obese [NIH 1998]). The moderate macronutrient composition diets—for example, LEARN (Lifestyle, Exercise, Attitudes, Relationships, Nutrition), Weight Watchers and Biggest Loser— led to about 8 pounds of weight loss. Considering that these diets are generally easier to adhere to, they could prove to be more effective eating plans for the long run. However, data beyond 1 year are not available, and the authors were unable to assess the degree of adherence to each of the plans.

The systematic review (Atallah et al. 2014) looked specifically at the weight loss and cardiovascular risk factor effects of four diets (Atkins, South Beach, Weight Watchers and Zone), based on a review of 12 RCTs. Some of these trials compared individual diets with usual care, while others compared the diets with one another. The researchers found that all diets led to some loss of weight, which was at least partially regained 1 year later. Weight Watchers was noted as the only diet that consistently led to weight loss that was at least partially sustained across all studies. Even then, the weight loss was moderate (8–10 pounds at 1 year), much of the weight was regained, and the results did not differ significantly from those of other diets when evaluated head-to-head. The diets that were reviewed appear to contribute to moderate improvements in blood pressure and cholesterol and minimal improvements to blood sugar measures. The number of quality studies assessing these measures is limited.

These findings are in alignment with each other and with most other high-quality diet studies, but not entirely. In fact, in the weeks preceding publication of the meta-analysis and the systematic review, a highly publicized RCT was published comparing a low-carbohydrate diet with a low-fat diet (Bazzano et al. 2014). This study found that a low-carbohydrate diet contributed to increased weight loss and an improved health profile at 3, 6, 9 and 12 months. A comparison of the meta-analysis (Johnstone et al. 2014) with the results of the new low-carb versus low-fat diet study shows that the amount of weight loss at 1 year was about the same for the low-carbohydrate diet (about 15 pounds at 1 year); however, in the new study, the amount of weight loss for the low-fat diet was lower (just 2–3 pounds). This study was fairly small—just 148 participants. It is unclear why weight loss on the low-fat diet was so much less in this study than in other RCTs.

The main takeaway from these studies is that it isn’t so much about which eating plan people follow to lose weight, but rather about whether they can cre- ate enough of a caloric deficit to lose weight and keep it off. While the “best- diet debate” may continue indefinitely, the preponderance of scientific evidence supports a clear conclusion: When it comes to weight loss, it doesn’t matter which diet a person follows, as long as he or she can stick with it. The weight loss is likely to be modest, and once adherence falters, much of the weight lost is likely to be regained. For information about how to coach clients on eating plans while staying within scope of practice, read the sidebar “Answering the Age- Old Question ‘So, What Do You Think About This Diet?’”

Food Quality

Of course, weight loss is not the only factor that clients should consider when preparing to make significant nutrition changes. The quality of food intake may go a long way toward optimizing overall health and quality of life. Independent of weight loss, high-quality eating plans such as DASH and Mediterranean enjoy a large body of evidence supporting their effectiveness in improving health parameters like blood pressure, cholesterol, blood sugar, cognitive function and other factors (Eckel et al. 2013; Rees et al. 2013; Wengreen et al. 2013).

For best results, a client who is over-weight or obese will consider a lifestyle change that incorporates 5%–10% weight loss and a health-promoting eating and exercise plan.

Each year U.S. News & World Report takes into consideration scientific evidence and expert feedback to rank 32
of the most popular diets. They are ranked according to these criteria: best diets overall, best commercial diets, best weight loss diets, best diabetes diets, best heart-healthy diets, best diets for healthy eating, easiest diets to follow and best plant-based diets (U.S. News 2014). Clients looking to start a diet may find this a useful resource in weighing the pros and cons and choosing a plan that best meets their needs. Rankings are available at http://health

A Two-Step Approach to Working With Clients

Fitness professionals commonly work with clients who are contemplating or already following various eating plans. When you are working with one of these clients, a useful approach is to listen carefully to the client’s reasons for following a particular eating plan; any positive and negative experiences with the plan to date; and what he or she says about adherence and commitment to the eating plan. The process of listening and withholding advice will help build rapport and strengthen your relationship with the client. As a general rule, offer advice or information only if specifically asked, or with permission.

Also carefully consider if there is any reason the client’s eating plan sounds unsafe or dangerous. If so, be more assertive. Refer the client to a registered dietitian or personal physician
Take the Quiz or mail the quiz on page 90. for further investigation and recommendations. If there is no reason to be concerned, support the client in his or her nutritional choice and be available to help optimize adherence.

From Diet to Lifestyle

Clients follow dietary practices for many reasons, most often because they believe that an eating plan will be particularly effective at helping them lose weight. In most cases, with proper planning, any of a variety of different types of eating patterns can be healthful and can contribute to weight loss, especially if the client is able to sustain the eating plan. Thus, a meaningful intervention is to help the client transform the diet into a lifestyle change by supporting adherence both to the eating plan and to a physical activity regimen, which is a well-established requirement for weight loss maintenance.

7 Ways to Help a Client Boost Adherence

Once a client has decided to make nutritional changes to support weight loss, you can play a key role in developing an action plan that is most likely to support those changes and contribute to long-term adherence.

following are seven strategies a client can use to support adherence to a particular diet, or rather “eating plan” or “lifestyle change.”

  1. Keep a food journal. Have the client keep a food log for 3 days, including 2 typical weekdays and 1 weekend day, prior to starting a diet. This will help the client identify baseline eating habits. Advise the client to measure portions and read nutrition labels. Help him find an app or a food tracker (a good quality, free one is www.supertracker to input the recorded information for a summary of calories, carbohydrates, protein and fat. Then, once on the diet, the client can periodically check in and compare current eating habits wit hteh diet’s suggested regimen.
  2. Be realistic. Help the client identify areas of change needed to adhere to the eating plan. If the changes feel too drastic, or the client has low confidence that she will be able to adhere to them, consider coaching her to identify the most realistic opportunities for change.
  3. Assess the home environment. For a client to adhere to an eating plan, the home environment has to support the plan. Help the client clean out foods that are inconsistent with the eating plan, and load up on healthier, nutrient-dense options. To support him in eating less, suggest reducing quantities and using smaller plates and utensils.
  4. Incorporate a doable physical activity program. A “doable” program is likely not only to provide results but also to be something the client actually enjoys and finds relatively easy to incorporate into her daily routine. The American College of Sports Medicine recommends 150-250 minutes per week of moderate-intensity activity for improved health and to prevent weight gain (Donnelly et al. 2009). This is equivalent to about three 10-minute activity bouts per day.
  5. Garner support. Social support is recognized as a very important predictor of weight loss success. Social circles also predict health behaviors. Help the client strengthen relationships with people who are like-minded and are practicing healthy behaviors. If those relationships do not currently exist, direct the client to appropriate social programs and groups. Encourage family involvement to the highest extent possible.
  6. Self-monitor weight. By keeping tabs on his weight, the client can see when regain begins and make the necessary adjustments to stop it. In fact, studies suggest this is a key behavior of people who lose weight and keep it off (Coughlin et al. 2013).
  7. Check in with a weight loss coach monthly. The Weight Loss Maintenance Trial found that the individuals most likely to maintain their weight loss had monthly personal counseling sessions incorporating nutrition and physical activity for at least 2 years. The sessions were brief and took place by phone (Svetky et al. 2008).
A Breakdown of Popular Diets

The following chart offers a quick reference to some of the most popular diets. Use it to help you guide clientstoward the best eating plan choices for them.

Atkins® low carbohydrate | calories not specified | induction phase with very low carbohydrates (20 g) and then gradual increase early weight loss | well studied with demonstrated benefit | recipes simple to prepare | good satiety and taste difficult to sustain | nutritionally deficient, especially in fiber and fruits | high in saturated fat
Biggest Loser® balanced | individual calorie targets | Adherents choose a Biggest Loser book to follow for instructions. emphasizes fruits, vegetables, lean protein and whole grains | discourages added sugar and solid fats | encourages home cooking | Exercise is a key piece of the program. Association with television show may create unrealistic expectations.
DASH (Dietary Approaches to Stop Hypertension) balanced | calories based on individual needs | high in fruits and vegetables | low sodium developed to reduce blood pressure well studied with clear health benefits | relatively easy to follow, with information and meal plans available for free ( may require retraining of taste buds, due to low sodium content
Gluten-Free balanced | calories not specified | eliminates all foods that contain gluten (wheat, barley, some other grains) treats celiac disease and may help those who believe they
have gluten sensitivity
not in itself associated with weight loss | poorly studied for those without celiac | Elimination of gluten could interfere with workup and diagnosis of celiac disease.
Jenny Craig® balanced | individual calorie targets between 1,200 and 2,000 | Followers purchase prepackaged meals and snacks and go to a Jenny Craig center for weekly counseling, or sign up for an at-home plan. Prepackaged foods make adherence easier initially. | meals well accepted by most people | behavioral support from peer consultant prepackaged foods very expensive and hard to sustain | does not allow for home-cooked and restaurant meals | Peer consultants are not health professionals.
LEARN (Lifestyle, Exercise, Attitudes, Relationships, Nutrition) balanced | calories not specified | emphasizes lifestyle changes to promote weight loss and health incorporates critical aspects of weight loss other than nutrition | self-taught | effective for long-term weight loss maintenance | promotes lifestyle change | well studied Initial weight loss may come slowly.
Low Glycemic Index balanced | calories not specified | a diet rich in “good carbs” (low glycemic index) emphasizes whole foods and minimizes processed foods difficult to know glycemic index of all foods | Studies show mixed results.
Medifast® balanced | very low in calories (800-1,000 per day) | five 100-calorie meal replacement shakes and Medifast products per day, plus one meat and vegetables entre╠üe per day Caloric restriction promotes quick weight loss. | nutritionally sound and balanced Because of the very low calorie levels, followers should have medical supervision. | difficult to sustain | minimal amounts of “real” food (uses powdered + water)
Mediterranean balanced | calories not specified |emphasizes produce, nuts, healthful oils and minimal red meat, sugar and saturated fat; red wine in moderation clearly has myriad health benefits | incorporates physical activity and exercise requires planning | may be more expensive than typical meals
Nutrisystem® balanced | calorie targets of 1,200-1,550 | Followers purchase prepackaged meals online and shop for vegetables and fruits to supplement them. Prepackaged foods make adherence easier initially.
| behavioral support in online group environment
prepackaged foods expensive and hard to sustain | does not allow for home-cooked and restaurant meals
Ornish low fat | calories not specified | rates foods as most (1) to least (5) healthful with emphasis on fruits, vegetables and whole grains group sessions for behavioral support | strong evidence for cardiovascular benefits | emphasizes exercise difficult to sustain | can be expensive
Paleo® low carbohydrate | calories not specified | Adherents aim to eat the way hunters and gatherers did, with no refined sugar, dairy, legumes or grains.
Emphasis is on meat, fish, poultry, fruits and vegetables.
discourages heavily processed and refined foods restrictive, which may lead to nutrient insufficiencies | not studied | expensive
Pesco-Vegetarian balanced | calories not specified | no meat or poultry; includes fish nutritionally balanced if well planned | heart healthy | Inclusion of fish provides additional benefit due to high health value of fish, especially oily/fatty fish. if not well planned, may have some nutrient insufficiencies, especially iron | People may miss meat.
South Beach® low carbohydrate | calories not specified | Initial low-carb phase relies on low-glycemic-index and high-protein foods, plus moderate
intake of mono- and polyunsaturated fats; gradually adds back “healthy” carbs.
differentiates healthful and less healthful carbohydrates | overall, healthy and balanced after first phase restrictive first phase | encourages too much initial weight loss | lot of time required for food preparation | not well studied
Therapeutic Lifestyle Changes (TLC Diet) low fat | weight loss calorie goals of 1,600 for men and 1,200 for women developed to decrease cholesterol effective at improving cholesterol | well studied | incorporates physical activity requires reading nutrition labels to meet saturated-fat and cholesterol goals
Vegan balanced | calories not specified | no meat, fish, poultry, eggs or dairy rich in high-fiber foods | provides health and environmental benefits very restrictive | risk of nutrient insufficiencies, especially iron and vitamin B12
Vegetarian balanced | calories not specified | no meat, fish or poultry nutritionally balanced if well planned | heart healthy if not well planned, may have some nutrient insufficiencies, especially iron | People may miss meat and fish.
Volumetrics balanced | calories not specified | emphasizes eating foods with low energy density (few calories relative to nutrient value/fullness) no food restrictions | filling | emphasis on vegetables and fruits may be hard to sustain, especially for people who don’t like fruits and vegetables
Weight Watchers® balanced | individualized calorie targets | tracks daily points (each point = approx. 50 kcal) based on current weight and weight goals good variety of foods | behavioral support | lots of education | not too restrictive | well studied with clear efficacy appeals to a specific audience | too costly for some | counselors, not health professionals
Zone® balanced | individual calorie targets | active weight loss targets of 1,200 calories for women and 1,500 calories for men lower in saturated fat than Atkins | recipes simple to prepare | effective in short term poor long-term adherence at least partly due to very low calorie allowance | restricts many nutrient-dense foods
Answering the Age-Old Question “So, What Do You Think About This Diet?”

Since there is no one “best” diet, and since adherence to a new eating and exercise plan is the most important predictor of whether someone will lose weight and keep it off, providing a simple answer to the question “So, what do you think about this diet?” is unlikely to be helpful. With adherence— rather than the number of fat grams or carbohydrates—being the most crucial factor, the objective changes from providing a client with information about which diet is best to supporting a client in making changes that he or she not onlyis ready to make but can feasibly sustain.

Therefore, when clients ask what you think about aparticular diet, ask if it would be okay if you posed a few questions to them first. Examples of questions are outlined below. These are the types of questions one might ask when using motivational interviewing as a communication technique, with the aim of providing two to three reflections for each open-ended question (this is demonstrated below with the first question). This approach is more likely to help a client gain insights into the change he or she is contemplating—insights that can then help you and your client work together to develop an adherence-enhancing action plan, should the client decide that now is a good time to make the change.

  • “What do you know about this diet already?” After the client answers this question, provide a couple of reflections of what you heard. For example, consider this hypothetical conversation:

    Client, who is considering starting a low-carbohydrate diet: “Well, I know that you pretty much eliminate carbohydrates. No more bread. No more pasta. No more rice. No more fruit, at least for a while. And then you lose a lot of weight.”

    Fitness professional: “So you know that if you make some of these changes to what you eat, you will lose weight.”

    Client: “Yes, I think so. I mean it would be hard to make all of those changes. But I know I need to lose weight. And I’ve heard the quickest way to lose weight is to follow a low-carb diet.”

    Fitness professional: “You want to go on a diet so you can lose weight, and you want to lose it quickly. But you know it won’t be easy.”

    Client: “Yes, right.”

  • “What is it about this diet that most appeals to you?”

  • “Based on your research, what changes do you think you’d need to make to follow this diet?”

  • “On a scale of 0-10, with 0 being not at all and 10 being absolutely, how ready are you to make those changes right now?”

  • “On the same 0-10 scale, how confident are you that you can sustain these changes for at least the next year?”

  • “So what do you think you’ll do?”

  • If during the questioning a client provides information that is factually incorrect or could potentially cause harm (for example, the client is considering taking a potentially dangerous weight loss supplement), refrain from overt correction; instead, ask the client’s permission to share the information. For example:

    “The eating plan you mention includes weight loss supplements. Would it be okay with you if I share with you a concern I have about weight loss supplements?”

    Overall, the client’s answers to these questions will help in assessing whether the client is ready to make a change, and if so, what changes he or she will be most likely to sustain. From there, if the client is ready, you can help him or her make plans to optimize adherence.


Atallah, R., et al. 2014. Long-term effects of 4 popular diets on weight loss and cardiovascular risk factors: A systematic review of randomized controlled trials. Circulation: Cardiovascular Quality and Outcomes.
Bazzano, L.A., et al. 2014. Effects of low-carbohydrate and low-fat diets. Annals of Internal Medicine, 161 (5), 309-18.
Coughlin, J.W., et al. 2013. Behavioral mediators of treatment effects in the Weight Loss Maintenance Trial. Annals of Behavioral Medicine, 46 (3), 369-81.
Donnelly, J.E., et al. 2009. American College of Sports Medicine position stand. Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Medicine & Science in Sports & Exercise, 41 (2), 459-71.
Eckel, R.H., et al. 2013. AHA/ACC Guideline on lifestyle management to reduce cardiovascular risk: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. doi: 10.1161/01.cir.0000437740.48606.d1/-/DC1.
Johnstone, B.C., et al. 2014. Comparison of weight loss among named diet programs in overweight and obese adults. Journal of the American Medical Association, 312 (9), 923-33.
Marketdata Enterprises. 2014. The U.S. Weight Loss & Diet Control Market (12th ed.). Lynbrook, NY: Marketdata Enterprises. 2014. Weight management: U.S. consumer mindsets. Accessed Jan. 6, 2015.
Wengreen, H., et al. 2013. Prospective study of dietary approaches to stop hypertension–and Mediterranean-style dietary patterns and age-related cognitive change: The Cache County Study on Memory, Health, and Aging. American Journal of Clinical Nutrition, 98 (5), 1263-71.

Natalie Digate Muth, MD, MPH, RD

"Natalie Digate Muth, MD, MPH, RDN, FAAP, is a board-certified pediatrician and obesity medicine physician, registered dietitian and health coach. She practices general pediatrics with a focus on healthy family routines, nutrition, physical activity and behavior change in North County, San Diego. She also serves as the senior advisor for healthcare solutions at the American Council on Exercise. Natalie is the author of five books and is committed to helping every child and family thrive. She is a strong advocate for systems and communities that support prevention and wellness across the lifespan, beginning at 9 months of age."

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