How healthy were 2019’s trendiest diets? A local expert weighs in

From the low-carb keto diet to intermittent fasting, here’s how local registered dietitian Joanna Pustilnik interprets them all.

a woman on a scale holding a burger in one hand and an apple in the other
© Maksymiv Iurii /

We live in a culture where brands like Weight Watchers and SlimFast are household names. 

Dieting is part of the social scene, and it’s not surprising with our reliance on social media how quickly new diets can seemingly pop up (and transform news feeds) almost instantaneously. 

In 2019, we saw the rise of the ketogenic (keto) diet, a low-carb and high-fat diet regimen that supposedly forces the body to burn stored fat rather than carbohydrates. We also saw the resurgence of Whole30, based on the New York Times bestselling cookbook, and a transition into flexitarian dietary patterns rather than strictly vegetarian or vegan. And who could forget intermittent fasting

To take a look back at this year’s trendiest diets, we spoke with Joanna Pustilnik of Mind Body Health LLC in Arlington, a registered dietitian and nutritionist. Find highlights from our conversation below. 

As a dietitian and personal-health professional, how do you feel about so-called “trendy” diets?

I usually have a healthy amount of skepticism when evaluating a new diet.  By definition, to be trendy or faddish is to be “intensely fashionable for a short time.” Humans are naturally drawn toward novel experiences, so trendy diets, offering promises of extreme or easy weight loss, are appealing. Clients often approach me with the desire to start their weight loss journey utilizing trendy diet guidelines, and I always share the research and try to encourage a more balanced, sustainable approach, such as intuitive eating. The problem is, traditional advice to “eat less and move more” is too vague for most people.

Unfortunately, trendy diets don’t come through on their promises and usually do more harm than good. In half of dieters, for example, post-dieting binges occur as a reaction to the diet-induced feelings of deprivation. In both my clinical experience, as well as what the research shows, dieting usually causes a slowed or sluggish metabolism leading to post-diet weight gain, less trust in our bodies, feelings of confusion about what or how much to eat, worsened body image and increased risk of disordered eating.

Do you find that those who jump on the bandwagon and start a trendier diet are successful, or does it fade away and people revert back to their old eating habits?

There is a plethora of anecdotal evidence supporting dieter’s success. On social media or Facebook, you are likely to find examples of people who have been “successful” on any particular diet, but we must exercise caution in how we define success. For example, imagine an image where there is a before and after picture, and the person has lost significant weight and looks happy. This is defined as dieting “success”, but weight change does not necessarily equal health or happiness. Research tells us that most people gain the weight back, and possibly more, after a year to a few years. In fact, dieting is found to be a consistent predictor of weight gain in long-term studies. Dieting can also cause bone loss, decreased muscle mass and metabolic issues. And often, the whole story isn’t shown in the photo. We can’t see if that person has developed hidden disordered eating patterns or increased anxiety surrounding meal choices or body image, which often occur when going “on a diet.”

Also, a thinner weight does not always equal a healthier person. We can be healthy at any size. People do usually return to previous eating habits, possibly with new onset bingeing or last-supper-type eating, and this yo-yo dieting increases risks for chronic diseases and a worse relationship with our bodies and our food.

What actually falls into the framework of dieting and what should readers know about it?

There is a difference between what we consider dieting and following a dietary pattern. A dietary pattern is a way of eating that is sustainable over a lifetime and typically doesn’t arbitrarily exclude whole food groups or dictate a caloric level. Dietary patterns are well-studied, and certain dietary patterns can be a successful way to improve our health. A recent study, for example, found Seventh-day Adventists, who follow a plant-based dietary pattern, have 30% lower risk of early death as well as a 30% lower risk of cancer. They also have a lower average BMI compared to the general population. The Mediterranean dietary pattern has also been shown to help decrease our risk of heart disease and cancer. Trendy diets usually don’t have the same level of evidence to support them. 

Potential benefits to dieting, however, are usually short term. Many people are motivated and excited when beginning a diet, full of hope and expectation. Dieting may also help people begin an exercise program as part of this enthusiasm. There also may be initial weight loss accompanying the diet, and for some, weight loss may be significant.

Diets center around deprivation which taps into primal hunger which often causes overeating, binges, cravings and subsequent guilt when we can’t “stick to the diet”. We are biologically wired to resist this deprivation so our metabolic rate decreases and hunger hormones increase. These changes don’t subside after we return to our regular eating so weight regain is the norm. 

Let’s break down the trendy diets of 2019. What is your take, and is any particular diet beneficial?

  • The keto Diet (also known as the ketogenic diet): The keto diet is 70% fat and less than 10% carbohydrates. It has been found to be beneficial for those suffering from epilepsy under the watchful eye of a doctor, but for long-term, successful weight loss, the evidence is just not there yet. I have many concerns about this diet, and I don’t believe it is a long-term solution. This diet is so low-carb that it triggers our body to use fat in the form of acidic ketone bodies, as well as protein from our muscles. This causes an acidic environment in our body which can be dangerous to our organs long term, and it can also cause muscle loss which will increase the risk of weight regain due to a decrease metabolism. Side effects of low-carb diets include fatigue, anxiety, depression. We need carbohydrates for energy, so this diet is hard to follow due to the cravings it naturally creates for these energy-producing foods. It is very difficult to follow for this reason and unappealing for many. High fat diets can also trigger insulin resistance.
  • Intermittent fasting: Intermittent fasting cycles between having  one or two days a week with only 500 calories (“fasting days”) and normal intake days where you eat what you want. Another approach is to only eating within an eight-hour period, and still another option is to fast for a full 24-hour period about once or twice a week. Fasting appears to be as beneficial as caloric deprivation on fasting insulin levels, and some research suggests it preserves lean muscle mass better than a low-calorie diet, but evidence is mostly in animal studies and not generalized. Anecdotal evidence from proponents of fasting diets suggest it is easy to follow, helps with increased energy levels and causes weight loss. Micronutrient levels may be difficult to reach, however, and side effects such as irritability, difficulty concentrating and fatigue are common on fasting days. Increased thoughts about food are common and distracting for many. Those at risk of eating disorders should steer clear. Socially, it can be very hard to follow.
  • The Mediterranean diet: I view this as a dietary pattern more than a diet. It has a large body of evidence supporting its use to prevent heart disease. It doesn’t cut out any foods or food groups, but it encourages fish, legumes, fruits, vegetables, nuts, and seeds, olive oil, and in moderation suggests low fat dairy and poultry. It limits added sugars and red meat as well as processed foods and other sources of saturated fat. It has been found to decrease inflammation and can cause weight loss due to its high fiber content. It is a balanced dietary pattern that doesn’t typically trigger feelings of restriction or a sense of being “on a diet.” Mediterranean cookbooks are full of satisfying and balanced plant-based meals with a focus on healthy fats. This is a way of eating with staying power, not a trendy diet.
  • Flexitarian diet: A flexitarian diet is a semi-vegetarian diet, and there is emerging evidence that it can help decrease body weight, improve metabolic health and reduce the risk of Type 2 diabetes. Plant-based dietary patterns such as this, as well as the vegetarian or vegan dietary patterns, are actually different levels of restriction within the plant-based dietary pattern. Vegans eat no animal products, vegetarians consume some eggs or dairy, and Flexitarians may eat some meat. The most important aspect of any of these is to utilize whole plant foods to obtain the plant chemicals, fiber, vitamins and minerals associated with greater health. Both veganism and vegetarianism are considered appropriate across the lifespan if planned well. We do not need animal products to meet our needs, and vegetarians and vegans have lower body weights as compared to meat-eating controls. Plant-based diets can improve mental health, positively impact our gut health, cut cancer risk, protect our heart, improve our blood sugars and they are also better for the planet. I routinely see my clients improve their health in all categories when they switch to a more plant-based diet. But we shouldn’t look at plant-based eating as a diet. How we think about our eating is important, and choosing to eat more plants and whole foods should be viewed as a lifelong goal instead of a trendy diet. Viewing it as a diet may trigger the same feelings of deprivation as other diets
  • Whole30: There isn’t much evidence to support this diet. It limits fruits, starchy vegetables, legumes, nuts and seeds, and is very high in meat for this reason. It can be difficult to follow and creates confusion about how to eat after the 30 days. I don’t view it as a way to “transform” our diet, because it isn’t a diet that considers our preferences, supports balanced intake or considers our ability to follow it long term. It is more a diet to promote short-term weight loss that, again, has all the risks of dieting—lowered metabolic rate, increased cravings, risk for emotional eating and weight regain. This fast-fix diet mentality is dangerous. I’ve had clients who have been on and off diets for decades with the resultant low self-esteem and yo-yo weight cycling only to finally hit rock bottom and decide they need to come face-to-face with the real problem—their expectation that diets work. There is no fast fix to health. We all need to examine our intake and life habits and make the needed changes over time to achieve weight loss and vitality.

When it comes to trendy diets in 2020, how should readers react and what should they know?

We should give up the idea that diets are a good idea. If this is difficult, I absolutely encourage finding a professional who is grounded in an intuitive eating, non-diet approach to help heal our relationship with food and come to a place of body positivity and health. If something is new and trendy, promising a quick fix, we should always use skepticism. 

What is your hope for readers and clients for a healthier 2020?

I hope we all begin to feel more confident in our bodies. I hope we are able to enjoy our foods and live in our bodies without guilt. I hope we can appreciate that health is independent of weight, and we should focus more on how we feel, not what we see on the scale. I also hope we will continue to value a planet-friendly, sustainable way of eating. 

Is there anything else readers should know?

The way we eat is very emotional, very visceral. We make food choices based on habits and history, but also on false ideas and untested theories. If you find yourself using words like “should” or “hate” in relation to food, I encourage you to reevaluate your overall relationship with how, why and what you eat. Often, it is not a new, trendy diet we need, but an honest assessment of how we feel about our food and our related beliefs.

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