5 Signs Intermittent Fasting Is Working for You—And 5 Signs It’s Not

From celebrities to CEOs, intermittent fasting (IF) has captured the attention of health enthusiasts and skeptics alike, promising a radical shift in how we approach nutrition and weight management. 

The main idea behind IF is that by cycling between periods of eating and fasting, you can help optimize metabolic processes and lose weight more easily, even without needing to count calories or give up your favorite foods. 

Several popular ways to practice intermittent fasting include alternate-day fasting and time-restricted fasting. Understanding how these methods affect your body can help you determine which approach is the best fit for your lifestyle—and, therefore, most likely to lead to benefits such as fat loss, appetite control, and improved digestion and insulin sensitivity.

That said, it’s possible this ever-popular trend just doesn’t work for you. Everyone is different! Here, we’ll explore signs that intermittent fasting is putting you on the right track to reach your health goals, as well as signs that it may not be the right approach for your body.

• ABOUT OUR EXPERTS: Dr. Joshua Axe, D.N.M., C.N., N.M.D., is a doctor of natural medicine, nutritionist, and the founder of Ancient Nutrition. Lena Bakovic, R.D.N., is a registered dietitian with Top Nutrition Coaching.

How to Practice Intermittent Fasting

Intermittent fasting involves alternating between periods of eating and fasting. The concept is simple: You restrict your eating to certain windows of time and fast (consuming just water and calorie-free beverages like coffee) outside those windows. 

According to Dr. Joshua Axe, D.N.M., C.N., N.M.D., a doctor of natural medicine, nutritionist, and the founder of Ancient Nutrition, three common intermittent fasting methods include:

• Alternate Day Fasting: You fast every other day, with very limited food intake on fasting days.
• Modified Fasting: You consume a very restricted number of calories on fasting days, typically about 25 percent of your usual intake, while eating normally on non-fasting days.
• Time-Restricted Eating: You reduce your eating to a specific time window each day, such as eating within a six or eight-hour window and fasting for the remaining 16 or 18 hours.

Why The IF Method You Try Matters for Your Results

People react differently to various fasting schedules based on their metabolism, lifestyle, and health status. What works well for one person may not be best for another, explains Axe. For example, someone who exercises vigorously likely won’t feel or perform their best on an intense fasting protocol. Same goes for pregnant and nursing women. Meanwhile, someone with low stress levels and a gentler exercise routine might thrive.

Some factors that influence your results, adherence, and overall experience when trying different fasting protocols, according to Axe:

• Varying metabolic responses: Longer fasts can promote deeper autophagy (the body’s process of cleaning out damaged cells and creating new ones), as well as significant fat burning, Axe says. At the same time, shorter fasting windows might be easier to maintain but may lead to less noticeable effects. Different fasting durations also affect insulin, growth hormone, and cortisol levels differently. These hormonal shifts can influence fat loss, muscle preservation, and energy levels.
• Impact on overall nutrient intake: Shorter eating periods might make it challenging to consume adequate nutrients, leading to issues like fatigue or brain fog, especially if you don’t eat nutrient-rich meals within your eating window, says Axe.
• Ease of incorporating it into your lifestyle: Stricter protocols might lead to better short-term results but could be harder to maintain long-term. They can also make social events, travel, and other variations from your day-to-day routine more challenging.
• Suitability for specific health goals or conditions: Axe finds that time-restricted feeding can help reduce snacking and nighttime eating and may support better sleep quality and blood sugar control. Meanwhile, studies show that both alternate-day fasting and time-restricted eating are safe tools for most adults that can produce clinically significant weight loss and improve several markers of metabolic health in those with obesity. The appeal of certain approaches largely depends on your intentions for fasting in the first place.

The bottom line? Understanding the factors above can help you choose which type of fasting approach best aligns with your goals and lifestyle, potentially leading to more successful and sustainable results.

Signs You’re Benefiting From Intermittent Fasting

While the effects of IF can vary from person to person, several indicators suggest the eating pattern is working in your favor. Recognizing these positive signs can help you stay motivated and confirm that your body is responding well.

1. Improved Energy Levels

When intermittent fasting works effectively, many people report an increase in energy levels. 

“With time-restricted fasting, for instance, the body’s metabolic processes align with the natural circadian rhythms, leading to more stable energy levels throughout the day,” explains Lena Bakovic, R.D.N., a registered dietitian with Top Nutrition Coaching. See ya, late-night snacking!

Research shows that IF can also help reduce systemic inflammation, which can also contribute to greater energy over time, she says. If you have more sustained focus and motivation and feel less tired, it may be a sign that your body is adapting well to your fasting regimen.

2. Easier Time Managing Your Weight or Losing Fat

A common goal of IF is weight loss or management—and if you’re noticing gradual positive changes in body composition, you’re likely fasting in a way that’s working well for your body.

Read More: Leptin Is The Weight-Management Hormone You Should Know About

“Some people experience weight loss and improved metabolic markers with intermittent fasting, especially with time-restricted eating patterns that align with their lifestyle,” Bakovic notes. Monitoring your weight and body composition are helpful ways of assessing the effectiveness of a given fasting routine.

3. Improved Mental Clarity

Many people find intermittent fasting enhances their mental clarity, productivity, and focus. Bakovic highlights that “intermittent fasting can improve cognitive function and concentration due to the stabilization of blood sugar levels.” 

Better cognitive performance overall while doing IF is a solid sign that fasting positively impacts your brain’s daily operations.

4. Stable Blood Sugar Levels

Been struggling to manage blood sugar issues?  Research suggests time-restricted eating can improve insulin sensitivity, Bakovic explains. This makes it easier for cells to absorb glucose from the bloodstream.

Time-restricted eating or periodic fasting can also help stabilize blood sugar levels by reducing the frequency of food intake and allowing the body time to regulate glucose.

This can result in healthier blood sugar management, which is good news for overall metabolic health, blood pressure, and the amounts of lipids (or fats) in the blood, according to Axe.

More balanced blood sugar might mean fewer spikes and crashes, often manifesting as fewer cravings for sweets and reduced fatigue and moodiness. Sound familiar? Your IF routine could be promoting better glycemic control.

5. Better Digestive Health

Improved digestive health is another positive sign of effective intermittent fasting. Bakovic notes that “allowing the digestive system to rest during fasting periods can improve gut health and reduce symptoms of bloating and discomfort.” Take note of whether you experience fewer digestive issues and enhanced gut function while sticking to a fasting routine.

5 Signs Intermittent Fasting Is Not Working for You

While fasting can potentially improve many people’s physical and mental health, it isn’t for everybody. According to Axe, certain groups of people—such as those who are already underweight, very stressed or sleep deprived, very active, pregnant, or who have a history of disordered eating—may be best off avoiding fasting due to potential side effects. Remember, there are a lot of variables (from personal health factors to different fasting protocols) here.

If you experience the negative symptoms below when fasting, consider trying a less intense approach or giving it up altogether and following a balanced diet with fewer restrictions. (And, yes, many of these are the exact opposites of the perks mentioned above!)

1. Persistent Fatigue and Low Energy

“Excessive fatigue and low energy levels can occur if the fasting period is too long or if nutrient intake is insufficient,” Bakovic warns. If you consistently feel drained while following an intermittent fasting regimen, it’s time to troubleshoot.

It could be that the particular fasting method is unsuitable for you and that you need to scale back to a more moderate form of fasting, suggests Bakovic. It could also indicate that you need to be more vigilant about consuming a variety of nutrients (and enough food overall) during your eating windows. Of course, make sure you are sleeping and hydrating well, as falling short in those areas can also leave you feeling wiped out.

2. Increased Irritability and Mood Swings

While fasting can support insulin sensitivity and glycemic control when the right people use the right approaches, it could lead to not-so-fun blood sugar changes if the approach isn’t a good fit for your body. 

You see, in some cases, extended fasts or very restrictive eating windows can lead to low blood sugar (hypoglycemia). For some people, low blood sugar leads to mood swings and irritability. (It can also cause symptoms like dizziness, confusion, sweating, or weakness, particularly if you are not consuming adequate fluids and electrolytes.) 

Read More: 7 Signs You’re Dehydrated

As such, frequent mood swings or crankiness could suggest that your body is experiencing fluctuations in blood sugar because of the fasting method you’ve chosen, suggests Bakovic. It could even be that your fasting regimen has caused you to fall too short on calories and nutrients, which also impacts your emotional well-being. If that hits close to home, consider adjusting your approach to fasting or opting for a more balanced style of eating.

3. Difficulty Concentrating

Struggling with mental fog can be a red flag that IF isn’t quite working for you (at least in the way you’re doing it). “When fasting leads to low blood sugar levels or inadequate caloric intake, cognitive function can suffer,” Bakovic says. 

Prolonged or extreme fasting periods are the most likely to lead to low blood sugar-related confusion and impaired concentration. Inadequate nutrient intake during fasting can also deprive the brain of essential nutrients, says Bakovic, while dehydration can cause headaches and reduced alertness. 

Additionally, fasting can elevate cortisol levels, potentially negatively affecting brain function in those who already experience high levels of stress (and therefore already have high cortisol).

If you experience persistent difficulty concentrating, sluggishness, and low motivation, reassess your fasting routine and consider making changes, such as shortening your fast and consuming more electrolytes to see if that helps, recommends Axe.

4. Unintended Weight Gain

“Weight gain can occur if your eating windows are filled with high-calorie, low-nutrient foods or if fasting periods lead to overeating,” Bakovic warns. Monitor your weight and food choices, and perhaps even your calorie or macronutrient intake, to pinpoint whether or not your fasting method supports your weight goals.

5. Nutrient Deficiencies

If intermittent fasting leads to insufficient intake of essential vitamins and minerals, nutrient deficiencies can pop up over time, says Axe. 

“Inadequate nutrient intake during fasting periods can result in deficiencies that impact overall health,” Bakovic agrees. Common symptoms of nutrient deficiencies can include fatigue, hair loss, and brittle nails. If you notice any of these, you may need to switch up your approach to improve your overall nutrient intake. 

Tips for Optimizing Intermittent Fasting

When fasting, stay attuned to your body’s responses, especially if you’re new to IF or the specific schedule and method you’re experimenting with. These best practices can help you find an approach to fasting that works for you.

• Choose the most suitable method: Choose a method that fits your daily routine and provides flexibility for your personal needs. “Time-restricted fasting is often more manageable and sustainable for many individuals compared to alternate-day fasting, for example,” Bakovic suggests. 
• Stay hydrated: Staying hydrated is key to feeling your best, especially during fasting periods in which you may be losing electrolytes without consuming many, explains Axe. “Adequate fluid intake is crucial to prevent dehydration and support overall health,” Bakovic agrees. Drink plenty of water throughout the day and consider incorporating herbal teas or electrolyte-rich beverages (think water with lemon and salt in it or calorie-free powdered electrolyte products).
• Focus on nutrient-dense foods: IF isn’t an excuse to eat junk, says Axe. He suggests prioritizing nutrient-dense foods, such as lots of veggies and protein, to meet your nutritional needs during feeding windows. Bakovic agrees that emphasizing a variety of whole foods—including lean proteins, fruits, vegetables, and whole grains—is the best way to support overall health and prevent deficiencies.
• Listen to your body: “If you experience persistent negative symptoms, consider modifying your fasting approach or consulting with a healthcare professional,” Bakovic recommends. Your body’s signals are essential for determining the effectiveness of your fasting routine, and you should never ignore signs like ongoing fatigue and weakness because you want the plan to work, Axe notes.
• Consult a healthcare professional: Before starting IF, it’s wise to consult with a healthcare provider, especially if you have underlying health conditions or take medications, Bakovic says.

The Bottom Line

A number of variables—including your personal health status and the type of fasting you try—influence whether following an IF protocol makes you feel like a million bucks or leaves you depleted. Tune into your body’s signals to gauge whether your approach is working for you or whether you’re better off sticking to a more typical approach to eating. Always consult with a trusted health professional before making significant changes to your diet, including going long stretches of time without eating.