Brian B. Parr, Ph.D., ACSM Certified Clinical Exercise Physiologist
Which diet is the best? This is one of the most common questions about nutrition and health, with implications for weight control, chronic disease prevention and treatment, and exercise performance. Unfortunately, there is no simple answer to this question. While there are certain eating patterns and various aspects of specific diets that are considered to be beneficial, there is no single “diet” that has been shown to be best for everyone.
As a general rule, healthy eating should be informed by nutrition science, not determined by the latest trends. Many fad diets raise concerns because they restrict or over-emphasize certain foods or nutrients, rely on meal replacements or supplements instead of real food, or are supported by limited evidence. The Paleo and Atkins diets are examples of popular diets that are at odds with traditional nutrition recommendations, and go against the “low-fat” advice we have long been provided. Given the popularity of these low-carbohydrate diets, it is worth exploring the benefits and drawbacks of each to help you decide if one of them could be right for you.
The Paleolithic diet emphasizes minimally-processed foods such as those that were consumed by our ancient (caveman) ancestors, emphasizing lean meat, eggs, fruit, and vegetables. While the diet restricts the consumption of grains and added sugars, the emphasis on vegetables, including root vegetables such as sweet potatoes, means that much of the energy comes from carbohydrates. That said – the Paleo diet is still lower in carbohydrates and fat and higher in protein than the typical American diet. It does, however, contain more healthy fats, like omega-3 fats. It is also much lower in added sugar.
These aspects of the Paleo diet contribute to certain health benefits, including weight loss and management of diabetes. The Paleo diet has a close connection with the health and fitness community through its widespread use by people who participate in CrossFit training. To be sure, some of the health and fitness gains are due as much to the exercise as the diet, but many aspects of the Paleo eating pattern seem to be beneficial even without CrossFit training.
By contrast, true low-carbohydrate diets restrict the consumption of nearly all carbohydrates, not just grains. The Atkins diet is the most famous example, but there are many others which limit carbohydrate intake to varying degrees. The emphasis of these diets is on protein and fat. Some vegetables containing carbohydrates are included in low-carb diets, but typically not starchy vegetables or grains.
Research seems to support the health benefits of diets that are relatively low in carbohydrates, especially refined grains and sugars, and relatively high in fat, especially monounsaturated and omega-3 fats.
Research seems to support the health benefits of diets that are relatively low in carbohydrates, especially refined grains and sugars, and relatively high in fat, especially monounsaturated and omega-3 fats. In particular, these diets are effective for promoting weight loss and treating diabetes, likely due to the restriction of refined carbohydrates and sugar. The next question is whether these diets are appropriate for people who exercise, either to get in better shape or to increase athletic performance.
The fact that so many CrossFit participants and competitive athletes follow the Paleo diet suggests that this eating pattern is consistent with their fitness and performance levels. The protein content is sufficient for promoting gains in muscle mass and strength for the vast majority of exercisers. Likewise, there are enough carbohydrates to fuel the intense training sessions for the majority of people.
Similarly, the low-carbohydrate diets, depending on how strictly they are followed, contain enough protein and likely enough carbohydrates to support training for most people, especially if gaining strength is a primary goal. However, athletes who train and compete at a high intensity, especially for long durations, require a high intake of carbohydrates prior to and during exercise to prevent fatigue and enhance performance. Extreme carbohydrate restriction may impair performance in some endurance athletes including distance runners, cyclists, and triathletes.
Despite the decades of research supporting the importance of carbohydrates for endurance performance, there are some scientists and athletes who are exploring how a low-carbohydrate diet can lead to adaptations that are consistent with this level of performance. This idea of becoming fat-adapted (or keto-adapted) is of great interest in the fitness community, although more research to support this concept, especially relative to long-duration exercise, is needed.
Something to keep in mind is that although the Paleo and low-carbohydrate diets may be consistent with fitness, weight control, and health, they are not the only way to achieve these benefits. Indeed, people who are considered to be fit and healthy have a wide range of eating patterns, from vegetarian and low-fat diets to extreme low-carbohydrate, ketogenic diets and everything in between. The one factor these people have in common is that they are active, leading to the conclusion that regular exercise is likely equally important to maintaining a desired level of fitness and health as eating patterns.
The bottom line is that you should match your diet to your individual health and fitness goals and personal preferences. Pick a diet that includes food you like and will eat, that fits into your lifestyle, and that you will follow, not by what is the latest fad. And remember, what the best diet advice of all, is to take a balanced approach to nutrition, eat real food, and not too much!
Brian B. Parr, Ph.D., ACSM Certified Clinical Exercise Physiologist, is an Associate Professor in the Department of Exercise and Sports Science at the University of South Carolina Aiken, South Carolina.