Why Keto isn’t Effective, Especially for Women

Many have heard about the Keto diet. You cut out carbs completely and you’ll magically lose weight!! Is it really magic though? Is this the trick we’ve been missing to lose fat?

Easy answer is; No.

Scientific answer is more complicated. There are many reasons why crash dieting isn’t great but specifically for Keto there’s 3 main problems; the way our body stores carbs, the metabolization of fat and the importance of carbs.

How Our Bodies Store Carbs

Many have seen success with the Keto diet because when we lose our natural carb storage that is saved in our muscles and liver, we also lose water weight as well. Water is always stored with carbs because it is heavily relied on to breakdown glucose into energy. For each gram of carbohydrates stored, there is 3-4 grams of water stored! So when you lose stored carbs you are losing 3-4x that in water as well.

However, if we're losing weight from our muscles and liver.... where is the fat disappearing? We don't store fat in those areas. Fat is stored adjacent to muscle in adipose tissue and in between muscle fibers but not within muscle. So the goal of weight loss is effective but we're not achieving the main goal of dieting. Losing FAT.

Metabolization of Fat

So how do we actually get rid of fat? There is never a simple answer but through many studies it is shown that when our body is performing moderate intensity exercise, that is the best state for the breakdown of fat. That's right; MODERATE.

Extreme intensity HIIT or sprinting will help your cardiovascular system and does have benefits for your body. But that is past the point where your body is comfortable enough to be in a state to start breaking down the stored fat. We need oxygen to breakdown fat and when we are working at 85-100% exertion, our body cannot take in enough oxygen to metabolize fat quickly enough as an energy source. Therefore, we use carbohydrates and limited stored energy because it is quicker and more readily available to help prolonged exercise. This causes us to become oxygen deficient and even after intense exercise we are trying to replenish the debt of oxygen we have overused.

This means that during and after intense exercise NO fat is being consumed. It is simply too much energy and time for our body to metabolize fat when the intensity is so high. If you happen to lose weight with repeated intense exercise, it is most likely carb storage and water being lost (just like in the Keto diet). Moderate exercise for longer than a few minutes puts our bodies into a state where we have used most of our stored energy in our muscles already and need more energy. Due to the intensity being lower than our maximum, we can reliably use fat as an energy source because we have enough oxygen supply and our body has enough time to utilize that macro efficiently.

I won't get into the boring cycle(s) of fat metabolization and all the steps involved because I even find it draining. But take away this, moderate exercise is ideal for fat metabolization and we need oxygen and glucose (carbs) to make it the most efficient source of energy. Also to achieve the ever so wanted fat loss.

Very simplified version on "How Your Food Becomes Fuel" taken from: https://www.thebodybuildingdietitians.com/blog/do-you-know-how-food-becomes-fuel

Another important factor of metabolizing fat is.....CARBS! Our bodies actually need pyruvate (which is the byproduct of carbohydrate breakdown) to be able to cycle through the Krebs cycle with the byproducts of fat metabolism (Acetyl CoA). This cycle is the longest cycle for our body to produce energy from but the most beneficial. We get the most energy from this source so our bodies ideally want to have enough time and energy to complete the process. Hence, why intense exercise is not ideal. Not enough time or energy, since our body is using so many resources in a short period of time.

Importance of Carbs

Our body needs carbs for neurological efficiency, energy for our muscles, fiber for proper digestion, blood sugar regulation and mood stability.

When food is limited, our body relies on those carbs stored in the muscles and liver to keep up with maximum brain function and so our muscles don't "hit a wall" and run on fumes. Stored carbohydrates is the fastest way our body can get energy within a short period of time when necessary.

But what about Ketosis???

Yes it is true that our body's will use fat as fuel (in the form of ketones) when we are in a state of ketosis, which in theory sounds great. However, there are more harmful effects of this than benefits to make this diet worth it.

Why it is Worse for Women?

More research is now coming out saying that women's bodies react differently than men's. A lot of the previous exercise science research was solely done on men in their peak fitness age and society accepted those findings as the general rule for all humans. Luckily, more work has been done to study women's bodies and their response to hormones, diets, exercise and more.

An interesting note found was that women actually metabolize fat differently then men. Since men generally have more testosterone and muscle mass, it is easier for them to burn more calories at rest, during the day, because the more muscle you have, the more fat you burn at rest. Also, the lower levels of estrogen in men help reduce fat storage. Due to hormones and fluctuation in energy levels during the menstrual cycle, women can be more fatigued without carbs and can have more vitamin and mineral deficiencies.

Another important finding is that thyroid hormones, specifically T3, TSH, TRH, are more sensitive to carb shortages and can actually affect the thyroid's overall functioning in women more than men. This SLOWS our metabolism which affects our bodies natural way of maintaining temperature, struggling with weight loss, increasing fatigue and even mental health instability. Long term shortages of these hormones have not been studied enough to have definitive answers on how drastic this can effect our overall health.

Closing Statements

It is evident to all my clients that I hate fad diets or anything where you are restricting something to the point of it not being sustainable long term. Weight loss should not be that difficult and its not a one answer fixes all. There are many different variables for each person and having a blanket statement diet is not good for the majority of us.

Specifically with the Keto diet, there is a lot of scientific evidence that discredits this popular widespread diet. Our bodies store carbs with water, when you are restricting carb intake you will lose the important stored carbs in your body, which means 3-4x that weight is being loss in water as well. Shockingly our bodies actually need carbs to fully metabolize fat! We need stored glucose (carbohydrates) with moderate exercise for successful fat burning. Lastly, carbs are important for overall neurological functioning, women's hormone health and balance in our bodies. Carbs are NOT your enemy.

One saving grace for us women is that it has been found that we burn fat more efficiently than men during exercise!! Our bodies have better responses to fat burning during exercise.

So there's your answer; Moderate exercise, not fad dieting.

References

Smith, D., Plowman, S., Ormsbee, M. (2023). Exercise Physiology: For Health, Fitness and Performance. Wolters Kluwer.

Blaak E. (2001). Gender differences in fat metabolism. Current opinion in clinical nutrition and metabolic care, 4(6), 499–502. https://doi.org/10.1097/00075197-200111000-00006

Iacovides, S., Maloney, S. K., Bhana, S., Angamia, Z., & Meiring, R. M. (2022). Could the ketogenic diet induce a shift in thyroid function and support a metabolic advantage in healthy participants? A pilot randomized-controlled-crossover trial. PloS one, 17(6), e0269440. https://doi.org/10.1371/journal.pone.0269440

Vranjić, P., Vuković, M., Blažetić, S., & Viljetić, B. (2025). Ketogenic Diet and Thyroid Function: A Delicate Metabolic Balancing Act. Current Issues in Molecular Biology, 47(9), 696. https://doi.org/10.3390/cimb47090696

Wu, B. N., & O'Sullivan, A. J. (2011). Sex differences in energy metabolism need to be considered with lifestyle modifications in humans. Journal of nutrition and metabolism, 2011, 391809. https://doi.org/10.1155/2011/391809