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How Effective—and Sustainable—are Popular Diets in Real Life? American Council on Exercise by American Council on Exercise Contributor

Specialized diets have become so common that it’s no longer unusual to find specific diet−related options on restaurant menus (such as gluten-free, dairy-free and vegan), or for dinner party hosts to ask their guests if they have any dietary restrictions that need to be accounted for. While some people follow restricted food plans for medical or health reasons, others do so by choice because they believe these diets will help them lose weight or live longer. This includes, among others, intermittent fasting (IF), paleo and the Mediterranean diet.

While these diets have been the focus of a growing body of research, particularly in terms of their effects on weight and longevity, many of these studies are conducted under the controlled setting of a supervised program. Currently, there isn’t a lot of research to demonstrate the effectiveness of these diets in the real world.

A research team at the University of Otago in New Zealand set out to close the gap of knowledge about the real-world efficacy of some of today’s most popular diets. Specifically, researchers sought to examine the long-term effects of following IF, paleo or Mediterranean diets in a real-world setting. Participants self-selected which diet they wished to follow, without any ongoing support from a dietitian.

Intermittent fasting (IF) involves limiting energy intake to about 25% of one’s usual diet (500 calories for women and 600 calories for men) on two self-selected days per week.

The Mediterranean diet encourages consumption of fruit, vegetables, whole-grain breads and cereals, legumes, nuts, seeds and olive oil, with moderate amounts of fish, chicken, eggs and diary and red meat once a week or less.

The paleo diet consists of mostly less-processed foods with an emphasis on eating fruit and vegetables, animal proteins, nuts, coconut products and extra-virgin olive oil. While “original” paleo diets strictly exclude all legumes, dairy and grains, this study used a modified version that included some dairy as well as up to one serving daily of legumes and grain-based food.

During the year-long study, which included 250 healthy adults with overweight and was published in the American Journal of Clinical Nutrition, researchers concluded that there were some weight loss and health benefits for adults with overweight who followed the Mediterranean, IF and paleo diets, though adherence to the diets dropped off considerably during the course of the year.

While IF led to slightly more weight loss than the other diets, the Mediterranean diet also improved blood sugar levels.

No Single, Right Diet

Co-lead author Dr. Melyssa Roy, a research fellow in the University of Otago’s Department of Medicine, says the amount of weight loss was modest—on average 4.4 to 8.8 pounds (2 to 4 kg), but those who followed the fasting or Mediterranean diets also experienced clinically significant improvements in blood pressure.

Dr. Roy says the evidence shows that, for some people, the Mediterranean, fasting or paleo diets can be “healthful, beneficial ways to eat.”

“This work supports the idea that there isn’t a single ‘right’ diet,” explains Dr. Roy. Rather, “there are a range of options that may suit different people and be effective. In this study, people were given dietary guidelines at the start and then continued with their diets in the real world while living normally.” Dr. Roy says that about half of the participants were still following their diets after a year and had experienced improvements in markers of health.

“Like the Mediterranean diet, intermittent fasting and paleo diets can also be valid healthy eating approaches—the best diet is the one that includes healthy foods and suits the individual,” says Dr. Roy.

Co-lead author Dr. Michelle Jospe, a postdoctoral fellow in the University of Otago’s Department of Medicine, says that, according to the results of their study, participants found the Mediterranean diet easiest to adhere to.

“Our participants could follow the diet’s guidelines more closely than the fasting and paleo diets and were more likely to stay with it after the year, as our retention rates showed,” explains Dr. Jospe.

Most of the 250 participants (54%) chose IF, while 27% chose the Mediterranean diet and 18% the paleo diet. After 12 months, the Mediterranean diet had the best retention rate, with 57% of participants continuing to adhere to the diet; by comparison, after one year, 54% were still fasting and 35% were still on the paleo diet.

After 12 months, participants who chose IF lost an average of 8.8 pounds (4.0 kg), while those on the Mediterranean diet lost an average of 6.2 pounds (2.8 kg) and those on the paleo diet lost an average of 4 pounds (1.8 kg).

Reduced systolic blood pressure was observed among those following the fasting and Mediterranean diets, together with reduced blood sugar levels in the Mediterranean diet.

Dr. Jospe explains that participants who said they were still following their diet at 12 months lost even more weight, showing the importance of choosing a diet that is sustainable. She believes the results of this study are relevant to the thousands of people following self-chosen diets with little supervision and indicates more realistic outcomes.

What This Research Means to Health and Exercise Professionals

Obesity remains a worldwide public health issue. More than 1.9 billion adults worldwide meet the criteria for obesity or overweight, according to the World Health Organization. It is associated with, and contributes to, a shortened life span, type 2 diabetes, cardiovascular disease, some cancers, kidney disease, sleep apnea, osteoarthritis and other conditions. Weight loss can lower the risk of developing these conditions and improve health outcomes. As a health and exercise professional, you are well positioned to provide the guidance individuals need to lose weight and, ultimately, reduce their risk of these diseases and improve their overall health and quality of life.

While your ultimate goal is to help your clients achieve permanent lifestyle change, helping clients who struggle with obesity lose as little as 5% of their body weight can go a long way toward improving their health and well-being. For this reason, the best answer to the question of which “diet” is best for weight loss is the one that an individual will be able to stick to long-term.

Of course, it is beyond your scope of practice as a health and exercise professional to offer specific diet plans to your clients. However, as with so much related to health and wellness, knowledge is power. Informing your clients about nutrition-related research empowers them to make healthy, informed decisions about the food they consume—not just in the short-term to lose weight, but in the long-term for overall health and wellness.

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