Why Low-Calorie Diets Don’t Help PCOS & What DOES

Why Low-Calorie Diets Don’t Help PCOS & What DOES

Why Low-Calorie Diets Don’t Help PCOS & What DOES 

As a clinician who treats PCOS, you are probably aware that diet plays a critical role in managing this condition. At its core, PCOS is a metabolic condition influenced by several factors–insulin resistance being one of the largest and most well established among them.  

So, while you know that diet plays a role in the treatment of PCOS, you might be surprised to learn that the diets you were taught about in medical school or your training for PCOS and its sister cousin–type two diabetes–are not only unhelpful but might even make these conditions worse. What are we talking about here? Low calorie and low-fat diets. Simply put, they don’t work–not for weight loss or for diabetes, and certainly not for PCOS. 99.5 percent of diets fail [1]. We don’t need to try very hard to convince you of this.  

Any practitioner has seen this in their clinical experience–better yet, anyone who has ever tried a diet has. We preach to our patients to eat less and move more and urge them to count their calories, but these strategies fail miserably. Despite strong evidence disproving its effectiveness, the portion-control, calorie counting strategy remains the “bread and butter” of what physicians recommend for weight loss. Jenny Craig, Nutrisystem, WW, etc. are all based on the same erroneous “calorie in calorie out” principle–meaning you store what you don’t burn–but this principle, while well applied in a closed physics system, doesn’t work so cleanly in real life for reasons we’ll soon explore.  

Low calorie, eat less, portion control–they are all more or less the same. This article will explore why none of these approaches work in the long-run and unveil strategies that can help your PCOS patients succeed long-term based on the latest, most compelling evidence.  

Why Low Calorie Is a Bust

As aforementioned, 99.5 percent or more of diets fail [1]. The million-dollar question is why? Is it simply because all patients are lazy and unmotivated? Hardly. Sure, some patients may be but surely not all of them. This failure rate clearly indicates something is wrong with the diet–not the patients we are unfairly blaming. So why do the calorie counting, constant restriction, frequent small meals, and portion-control focused approaches fail us? There are two simple reasons: 

1. They Are Too Constant

With a low-calorie approach, patients are expected to eat the same low number of calories per day. This creates a problem when it comes to insulin. By telling patients to eat 5-6 small meals per day, we are continuously spiking insulin all day long. Think of insulin like a water faucet; it is either off or on. Whether the faucet is open a little or a lot doesn’t matter because the water is still running. Insulin is still there instructing the body to store fat, inhibiting lipolysis, and driving the metabolic dysfunction of PCOS, whether we eat a little or a lot. And with constant exposure to insulin, we drive insulin resistance [2]. 

This effect can be observed in nature–such as drug resistance, antibiotic resistance, and many other examples. As the body, organism, etc. adapts to an input (drug, person’s immune system), resistance is built up that must be overcome with higher doses (drug resistance), or different, stronger antibiotics (antibiotic resistance)–you get the picture [3]. Hormones work at specific and limited times to prevent such resistance. For instance, cortisol and testosterone are highest in the morning. Melatonin and Human Growth Hormone is highest at night. If these hormones were always coursing through our systems, we would quickly become numb to their effects [3]. This is exactly what happens when we encourage patients to eat–albeit low calorie–all day long. Insulin resistance is only made worse which triggers compensatory hyperinsulinemia which then triggers weight gain and worsens PCOS in a vicious cycle.  

As evidence, a six-month study compared the effects of daily caloric restriction to intermittent fasting, keeping total calorie intake the same. While both groups lost the same amount of weight, the intermittent fasting group experienced a much greater drop in fasting insulin and insulin resistance–which is key to long-term management of PCOS, as well as weight loss and diabetes prevention [2]. Other studies comparing intermittent fasting to daily calorie restriction often note greater fat and/or visceral fat loss and increased lean body mass in the fasting groups compared to the groups assigned daily restriction[2]!  

2. Compensatory Adaptations –Eat More, Burn Less

With constant calorie restriction, the body doesn’t know when it will get its next meal, so it compensates by decreasing the metabolic rate and increasing hunger–efforts which derail any hopes of weight loss [2]. Even with strict calorie restriction, the body can quickly adapt by burning several hundred calories less over time, as evidenced by numerous studies, such as the famous Minnesota Starvation Experiment.  

What Does Work:

  1. Low Carbohydrate Diets  
  2. Ketogenic Diets  
  3. Protein-Rich Diets  
  4. Intermittent Fasting  
  5. Low Glycemic Diets discussed in future article  
  6. Fasting Mimicking Diet discussed in future article  

Why Does It Work?

These diets can be used alone or in conjunction for synergistic benefits. While they may differ in their approaches, they all reduce the insulin resistance and hyperinsulinemia that drives PCOS. Rather than focusing on chronic calorie restriction, these diets focus on a macronutrient composition that is least likely to spike insulin or emphasize meal timing to reduce insulin spikes rather than “calories in calories out” which views a chicken and kale salad as equivalent to a glazed donut in their net metabolic effects as long as they are equal in calories–but nothing could be further from the truth [4]. So, what is the evidence behind these dietary approaches for PCOS?  

Low Carbohydrate and Ketogenic Diets

All carbs–whether starchy or sweet–are quickly broken down into simple sugars, which require large amounts of insulin to metabolize. Since patients with PCOS produce excessive insulin and are insulin resistant, a low carbohydrate diet lowers the need for insulin, thereby restoring insulin sensitivity.   

Low carb diets also tend to promote greater satiety than traditional, low-calorie diets–likely because they are higher in appetite suppressing fat and protein [5]. On a low carb diet, patients can eat until they are comfortably full and still lose weight. Low carb diets may even significantly increase the number of calories burned at rest by upwards of 300 calories or more per day, according to a landmark study BMJ [6]! That is equivalent to an hour or cardio. Ketogenic diets confer even greater benefits beyond a modest low carbohydrate diet by putting the body into nutritional ketosis [7].    

Intermittent Fasting

Intermittent fasting solves the problem of constant insulin release. By limiting the time spent eating to a fixed window (i.e.- a 4-hour window, every other day, etc.), insulin spikes are reduced and sensitivity to insulin is restored [8]. Intermittent fasting also prevents the body from viewing food as scarce because the restriction isn’t constant, so compensatory hunger and decrease in metabolic rate do not occur as readily [8].  

In fact, some research shows that intermittent fasting can even decrease ghrelin, the hunger hormone, and increase leptin, the satiety hormone; the same cannot be said for constant calorie restriction [9]. Lastly, contrary to popular belief, fasting does not put patients into “starvation mode” Instead, it increases metabolic rate thanks to an impressive concoction of fat-burning hormones, including growth hormone, adrenaline, glucagon, T3, and more [8][10].  

For best results, encourage your patients not to overeat during their eating window and to still emphasize healthy foods when they are eating.   

Protein-Rich Diets

Diets rich in protein (~25-40 grams per meal) are beneficial for PCOS because protein has a much milder impact on blood sugar compared to carbohydrates and promotes satiety. The body burns about 30 percent of the calories found in protein just to digest it [11]. Protein also increases the release of the satiety hormones Peptide YY, GLP-1, and cholecystokinin (CCK) and decreases ghrelin. It has been shown by several studies to curb appetite. However, excessive protein can raise blood sugar and insulin levels too, so balance is key.   

What’s Next?

Now that you understand why the low calorie, portion-control approach will not help your PCOS patients–at least not long term–you can begin using dietary tools that actually work, improving both immediate issues like anovulation and long-term concerns like diabetes.  

We’ll explore more treatments for PCOS over other blog posts and in our EBook: Your Ultimate PCOS Toolkit, where we will dive into exciting topics such as helpful biometrics for diagnosing PCOS and case studies for real life application–an indispensable addition to your understanding of PCOS and how to treat it.


  1. Fildes A, et al. Probability of an obese person attaining normal body weight: cohort study using electronic health records. Am J Public Health. 2015;105(9):e54-e59 
  2. Fung J. Chapter 15: Intermittent Fasting. In: Kenward L, Melcombe L, eds. The Diabetes Code. Prevent and Reverse Type 2 Diabetes Naturally. Vancouver/Berkeley: Greystone Books; 2018:191-195.  
  3. Fung J. Chapter 6: Insulin Resistance: The Overflow Phenomenon. In: Kenward L, Melcombe L, eds. The Diabetes Code. Prevent and Reverse Type 2 Diabetes Naturally. Vancouver/Berkeley: Greystone Books; 2018:58-66 
  4. Fung J. Chapter 15: Intermittent Fasting. In: Kenward L, Melcombe L, eds. The Diabetes Code. Prevent and Reverse Type 2 Diabetes Naturally. Vancouver/Berkeley: Greystone Books; 2018:198-199.  
  5. Gibson, A.A., Seimon, R.V., Lee, C.M.Y., et al. (2015), Do ketogenic diets really suppress appetite?. Obes Rev, 16: 64-76. https://doi.org/10.1111/obr.12230 https://onlinelibrary.wiley.com/doi/abs/10.1111/obr.12230  
  6. Ebbeling C B, Feldman H A, Klein G L, et al. Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial BMJ 2018; 363 :k4583 doi:10.1136/bmj.k4583 https://www.bmj.com/content/363/bmj.k4583  
  7. Spritzler F, Tamber M, Scher B.The complete guide to ketosis. Diet Doctor. Updated on February 22, 2023. Accessed August 11, 2023. https://www.dietdoctor.com/low-carb/ketosis  
  8. Fung J. Chapter 15: Intermittent Fasting. In: Kenward L, Melcombe L, eds. The Diabetes Code. Prevent and Reverse Type 2 Diabetes Naturally. Vancouver/Berkeley: Greystone Books; 2018:191-198.  
  9. Hutchins R. Does Intermittent Fasting Work? UNC Health Talk. March 13, 2019. Accessed August 10, 2023. https://healthtalk.unchealthcare.org/does-intermittent-fasting-work/#:~:text=Ghrelin%20is%20the%20hunger%20hormone,which%20is%20the%20satiety%20hormone 
  10. Fung J. Chapter 20: When to Eat. In: van Emden E, ed. (Why your body’s own insulin is the key to controlling your weight)The Obesity Code. Unlocking The Secrets of Weight Loss: Greystone Books; 2016: 238-241.  
  11. Gunnars K. How Protein Can Help You Lose Weight Naturally. Healthline. Updated on March 30, 2023. Accessed August 4, 2023. https://www.healthline.com/nutrition/how-protein-can-help-you-lose-weight