Is a calorie deficit necessary to lose weight?


Is it necessary to eat at a caloric deficit in order to lose weight? Could a low-carb diet be to blame for lost periods? What could be the reason for absence of weight loss? And what could be the cause of high blood sugars during your period?

Get the answers to these questions in this week’s Q&A with fertility specialist Dr. Fox:

Is a calorie deficit necessary?

Dr. Westman and others have said that ‘of course calories do matter’. Does this mean that we need to achieve a deficit of 500 calories a day, whilst also consuming 20 g of carbs?


Dr. Fox:

While calories do ultimately matter, the idea that any animal will exactly match their caloric needs with caloric intake I think is untenable. Animals in the wild certainly are not counting calories. It is my belief that if one is purely ketotic, that weight loss (assuming overweight to start with) will ensue almost no matter what the calorie intake overall to a point of homeostasis.

If you were a caveman who was fed corn for six months and “fattened” as we would cattle, then you would likely return to the exact ideal body weight. In today’s world however, especially for women who may be more sensitive to stress, there are upward pressures on weight caused by stress and cortisol elevation. Because of this, the homeostatic point for weight will fall short of ideal body weight. This frustrates everyone very much.

Stressors for women include excessive aerobic exercise, sleep disturbance, sleep apnea, circadian rhythm disruption, caloric restriction (in high-carb nutritional environment), caffeine and nicotine, Type A personality, “connectivity stress” (cell phone, email, texts, Facebook, Pinterest etc etc), work stress etc. Things like yoga, walking, acupuncture and meditation can relieve those stressors in addition to addressing them individually. Lastly, hormonal competency or normal estrogen levels are absolutely critical to be able to achieve complete metabolic health. The issue of metabolic health is a complex one and there is no “simple answer.”

As patients get closer to ideal body weight, some calorie restriction might be helpful but I am not an advocate for constant or prolonged fasting for women due to the stress that may follow this. If you want to do a 48-hour fast once every couple of months, I think that is OK however, the rest of the time you should have adequate calories for daily needs.


Periods have stopped after eating low carb

My 14-year old daughter has had fairly regular periods for two years now. She started eating low-carb approximately six months ago due to some food intolerances and skin issues she was having. Those symptoms are now sorted and she’s the healthiest physically that she’s ever been. However, three months ago her periods stopped completely.

She has not lost any weight since going low carb, though she may have lost some “fat” (her breasts have become slightly smaller) but she has always been quite small for her age. She currently weighs 47 kg (104 lbs) and is 161 cm (5’3″) tall.

Are her lack of periods something to be concerned about or is this a common occurrence when starting a low-carb diet for someone her age?


Dr. Fox:

Great question: No, I would not think low-carb high-fat would cause stress enough to lose periods or cause significant delays. Excessive exercise is the single most common reason for women to have cycle irregularity or loss of periods.

Also is she getting enough calories? (See my answer to Rosemary above). Relative starvation is common among teens. Their friends are feeding them the party line of calorie restriction to solve weight problems, so better look into this. She may need an evaluation for this with thyroid and other endocrine problems as more unusual causes.

Good luck.


Frustrated because of no significant weight loss


I have been eating keto since 3/18/2019. I know that I am in ketosis using my meter. However I have only lost 9 lbs (4 kg). I have not cheated once! I am a physician and I am perplexed because it seems that my body does not seem to respond as well as most people.

I am s/p sleeve gastrectomy in 2011 and went from 286 lbs (130 kg) to 185 lbs (84 kg) and maintained my weight until 1.5 years ago through a balanced diet and regular exercise. I became ill and was sedentary and gained some weight. I decided to try keto and became more active.

I am stressed out and wonder whether my cortisol levels or a low BMR have anything to do with this.

I also wonder whether I am getting too many calories…

I’m super frustrated, but I feel proud that I have not given up. This has been the first lifestyle change that seems sustainable. I feel satisfied and do not have many cravings and I feel more energetic and have less aches and pains.

I also wonder whether all this dairy may have something to do with it.

I would really appreciate some advice.

Thanks in advance,

Dr. Fox:

Thanks for great questions and I apologize for delayed answer. In my opinion, bariatrics and the ensuing weight loss works through a starvation mechanism, that like anorexia produces intense physiologic stress and sensitizes you in a hypothalamic way. See my other answers for in-depth discussion of physiologic stress. Your baseline system will have a decreased BMR and you now are extremely sensitive to other stressors.

No matter what you will see health benefits to this approach even without weight loss as you described so that is a positive gain already. Now that you are hypothalamically predisposed, you need to avoid excessive aerobic exercise; walking and mild resistance training are OK, but don’t over do it. You should also consider stopping caffeine, as this can double your cortisol.

Give it more time and your system may begin to change. Remember, your dysfunction lasted a long time and resolution may take time as well. Look at all your carbs. Most of our bariatric patients are not able to tolerate more than 15, or maybe 20 grams, of total carbs per day. No sweeteners like many of the websites and recipes discuss. Get 7-8 hours of sleep and don’t work night shifts. Best of luck – hope this helps.


Should blood sugars be lower during a period?

I recently took to measuring my blood sugars and blood ketones.

I had always assumed that during ones period, one should have higher blood sugars because I mean, I personally gain 3 pound (1 kg) during my period. I am astonished to find that although my fasting glucose (measured 12 hr after low carb – of course! – meal) are usually in the low 80 mg/dl (4.4 mmol/L), it plummets to upper 50’s/low 60’s mg/dl (2.8 – 3.3 mmol/L) during my period!

I mean either something’s wrong with me or I assumed wrong.

Is it ok for blood sugars to fall during ones period? What is the reason behind the weight gain during ones period? How low can the blood sugars get without it being problematic? Is it advisable to raise ones carb count during the period to have more “normal” blood sugar levels?


Dr. Fox:

Wow, some great observations and questions! Yes, physiologically there is a reason for all this, and it is simply the progesterone effect in addition to a very low estrogen level during the cycle. This combination creates an increase in insulin resistance as does pregnancy, causing blood sugars to fall faster and lower. Remember in ketosis, humans can tolerate sugars much lower than in a high carb environment. One strategy would be to eat at least 150 calories every 2-3 hours on those days if you seem symptomatic at the lower BS levels. By no means would I suggest increasing carbs to “compensate.”


More questions and answers

Questions and answers about low carb

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