Let's Chat About Fasting

Fasting can be very Good. Underfuelling can be very Bad. They are not the same thing   

I’m writing this in response to questions I often receive from clients, such as:

• How can I lose weight without causing metabolic damage?
• Is fasting bad for women?
• Is fasting beneficial if I’m not trying to lose weight?
• Does fasting harm hormones?
• Is fasted exercise bad?

Let’s be clear about four things;

1. Fasting has benefits beyond weight loss.
2. Fasting doesn’t necessarily equal weight loss.
3. Fasting and underfuelling are not the same thing.
4. When performed correctly, fasting can support health—whereas long-term underfuelling does not.

Now remember I am not a doctor, and as I say below fasting isn’t suitable for everyone.  people with certain conditions aren’t advise to fast and you should check with your GP is you have any health conditions  Also beware of rearranging your life and changing behavior after reading any one book, article or podcast! 
If you’ve read my previous blog on the dangers of RED-S and hypothalamic amenorrhoea (HA), you’ll know that chronic energy deficiency can have serious consequences, particularly for hormonal and reproductive health—for all genders, but especially for those who are biologically female.
But correctly applied fasting does not automatically trigger these issues. In fact, quite the opposite: when done properly, fasting can support metabolic health and hormonal balance.
**What Is Fasting? Fasting: A Tool, Not a Deficit**
Fasting, when done correctly, is a planned period without calorie intake or insulin stimulation. It gives your digestive and metabolic systems a purposeful rest.
Research shows that fasting can:

• Improve insulin sensitivity
• Reduce insulin resistance
• Promote autophagy (cellular repair)
• Support fat metabolism and appetite regulation
• Enhance mental focus

Fasting will not harm your metabolism, stress your adrenals, or cause malnutrition—unless it’s overdone or paired with insufficient nutrition.

What counts as “overdone” or “done incorrectly” is highly individual and depends on age, gender, lifestyle, goals, health status, weight, and activity levels.

Fasting must be followed by nutritious feasting to prevent underfuelling and its consequences.

Fasting is a controlled pause, not a starvation state. During your eating window, you should refuel with nutrient-dense foods that restore energy, nourish your body, and replenish your stores.

Common Fasting Protocols
There are many protocols when it comes to fasting and the right approach for you is very personal and depends on your goals and lifestyle and experience   
The easiest, safest, and most widely used method is:

• Time-Restricted Eating (TRE)
Examples: 12:12, 14:10, 16:8, 18:6.
A 12:12 window means you fast for 12 hours (water allowed) and then eat for 12 hours.
TRE is simple, sustainable, and works well with natural circadian rhythms.
The length of the eating window can be adjusted to fit your needs.

Underfuelling: When Fasting Becomes potentially Harmful
Underfuelling occurs when your daily intake of energy and nutrients is consistently below what your body requires—whether you are fasting or not.

Consequences can include:

• Loss of lean muscle mass
• Hormonal imbalances (thyroid, sex hormones, cortisol)
• Fatigue, irritability, poor concentration
• Reduced athletic performance
• Increased injury risk and low bone density
• Impaired immunity

As previously discussed, chronic underfuelling can lead to RED-S and HA, with long-term implications for bone health and fertility.
Unlike strategic fasting, underfuelling is not intentional or beneficial—it is an ongoing energy deficit that stresses the body.
How to Fast Without Underfuelling
The goal is to access the benefits of fasting while meeting your nutritional needs.
1. Prioritise nutrient-dense meals
During your eating window, do not diet. Eat a wide variety of colourful whole foods, including protein, healthy fats, complex carbs, vitamins, and minerals.
Avoid ultra-processed foods—but don’t restrict carbs, fats, protein, or calories.
2. Time your exercise wisely
Consider arranging your eating window so you can fuel around workouts.
Opinions vary on this, but if you want to proceed on the side of caution, it’s a sensible approach.
I personal feel early eating windows are better for multiple reasons especially hormone support  but research again is mixed on this topic 
3. Listen to your body
Hunger, dizziness, or persistent fatigue indicate that your fasting protocol needs adjusting. Don’t ignore these signs.
4. Match your fasting window to your personal needs
If you’re very active, shorter eating windows (e.g., 18:6) may make it difficult to consume enough food.
Adequate intake is essential.
Side note: If weight loss is your goal, see the end of this blog.
For women, reassurance is simple:
Hormones and metabolism thrive on adequate nutrition, and they can tolerate the occasional missed meal.
Fasting becomes problematic only when energy intake is chronically low to support your energy needs   

If you’re hungry, eat.
If you’re not hungry, don’t eat.
Don’t skip meals and then compensate with milky coffees or low-calorie snack bars. But don’t fear missing a meal either.
If you choose to explore fasting:

• Avoid a “dieting mentality” during eating windows. Feast! 
• Eat plenty of nutritious, variety minimally processed foods 
• Don’t restrict non processed macros: carbs fats or protein 
• During fasting windows, consume only plain water, black tea, or black coffee.
  This is known as a clean fast. Milk in coffee is food, zero calorie drinks Sike insulin so these are only for eating windows. 

The Bottom Line
In my humble opinion, and according to current research:

• Fasting is a powerful tool when used intentionally.
• Long-term underfuelling is harmful.
• The two are not the same—and they can coexist safely and effectively.

Authors and “Experts” such as:

• Stacy Sims
• Mindy Pelz
• Gin Stephens

…may differ in their views on fasting for women, but they all agree on one thing:
Having regular time off eating—a minimum of 12 hours a day—is beneficial for everyone for long-term health.
If you have any questions after reading this, send them to me. I’ll answer them in a future blog—and if I don’t know the answer, I’ll research it and share what I find.
“ahem…..”
But what If Your Goal Is Weight Loss? Don’t you need to eat less than you burn to achieve this? 
Great question ! 
Watch out for my next blog which will tackle the complex subject of weight loss.