People often wonder why one person feels and looks amazing on a diet while it leaves another person hungry and frustrated. Nutrition is a complex, deeply individualized science that cannot be boiled down to a simple formula. The media tries to claim one specific plan will help everyone look or feel a certain way. Unfortunately, these trendy diets take out the individualization of nutrition.

Here is a breakdown of a few fad diets and why they may or may not work for everyone.

Intermittent fasting (IF) has become incredibly trendy because many find it easy to follow. There are many ways to execute IF, but most popularly, one chooses a fasting window for anywhere from 10 to 20 hours per day. For example, one could fast from 6 p.m. until noon the following day for an 18-hour fast. There is amazing evidence showing incredible benefits from this eating pattern. Research shows it can help to promote weight loss, improve blood sugar balance, decrease inflammation and increase cellular health. However, in practice, there can be some negative consequences to IF.

For example, some menstruating or peri-menopausal women can find that IF will disturb their hormonal imbalance, change their cycle length, or block ovulation. Women’s bodies are primed for reproduction secondary to survival. IF can create an unsafe or stressful status in the body, altering their menstrual cycle. Furthermore, women that already have imbalanced cycles should not attempt IF.

Additionally, individuals under increased emotional or physical stress should not practice IF. Just like running a marathon every day would be too stressful for the body, long bouts of fasting can increase stress in the body. Other signs that IF may not be appropriate include lack of hunger/fullness cues, increased headaches, loss of muscle mass, worsened sleep, increased or existing anxiety, pregnancy, history of eating disorders, or adrenal/cortisol imbalances.

The keto diet is based on eating primarily fat, some protein and minimal carbohydrates. Like IF, magazine covers frequently have men with six pack abs claiming that the keto diet helped them “get shredded”. However, a common misconception is that the keto diet should be a forever diet. Biologically speaking, one should not be following the keto diet indefinitely. Individuals following the strict rules of the keto diet often stop because it is unsustainable and then gain weight right back.

The keto diet can be used as a tool once the foundations of a balanced diet and lifestyle are addressed. Start by incorporating healthy fats at each meal and decreasing the amount of added sugar consumed per day. This gentler approach to the keto diet will likely yield longer lasting results.

Viewing the vegan diet from a primarily biological perspective as a dietitian, some individuals do better on a vegan diet than others. This is due in part to our unique genes. For example, when we eat omega-3 fats from vegan sources, we need to process and convert them to the anti-inflammatory form that we tout for heart and brain health. Genetically, some are great at this conversion and others are not. People with anxiety, depression or severe gut bacterial imbalances may struggle with a vegan diet to get the proper amounts of nutrients to eradicate these imbalances. Even carnivores can take vegan principles into consideration, prioritizing fruit and vegetable intake with higher- quality meat portions alongside.

The perfect diet does not exist. Based on genetic factors, lifestyle and other health conditions, individuals should work to find a diet that maximizes their health goals. Most importantly, stay open to adapting eating habits based on different life stages and work with a functional dietitian to help identify personalized nutrition do’s and don’ts.