Calories and Your Metabolism Slows?
We’ve all heard that you can slow your metabolism by eating too few calories. But at what point does this “slow down” in your metabolism happen? I recently got asked an excellent question from a CGB reader regarding this subject.
Question from Dax: Hey, I really like your website . . . and I’m a guy, is that okay? I understand the science behind the slower metabolism on a restricted diet. Your body becomes more efficient, which sounds like a good thing, but actually means that you run on few calories and, therefore, more calories would become fat.
However, I get confused by the numerous examples of the opposite. Why did Christian Bale in the Machinist get so thin! He claims he lost 63 pounds by eating nothing other than a can of tuna and an apple per day. Why didn’t his metabolism keep him from losing the weight? (Pic is of Christian Bale before and after his weight loss)
Also, what is the fewest calories a man can eat without going too low?
Answer from Martha: First, I think it’s great that you enjoy my blog! I actually have a lot of male readers. I try to make many of my posts of interest to both guys and girls. Second, you asked an excellent question that I have actually wondered myself. While I don’t have a scientific answer for you, here are my thoughts…
Studies have demonstrated that the metabolism does slow when the caloric intake has been decreased to a very low level, especially when this restriction has been ongoing AND a fair amount of weight loss has occured. The act of losing weight in itself will slow the metabolism. In addition, the new lower body weight will require fewer calories that the initial higher body weight. So this is a double whammy so to speak.
But you have raised a good point. How can some people, such as Christian Bale or anorexics, get to such a low body weight if their metabolisms slow down? My answer would be that they consume SO FEW calories that they still lose weight despite the slow down in metabolism. Many anorexics consume only 400 calories a day and may exercise for several hours a day. Christian Bale’s diet doesn’t sound far off from 400 calories. BTW – check out this link for more info on Christian Bale’s 63 pound weight loss for the movie The Machinist. Another example would be liquid diets. I worked with these medically supervised fasts, such as Optifast, for many years when they were popular. The participants generally started out obese and ate only 500-800 calories a day (in the form of shakes) for months at a time. If they stuck to the diet, the majority of them lost a large amount of weight. So despite the slow down in their metabolic rate, they were still able to lose weight. But here is the problem – when they start to eat even somewhat normally … their weight skyrocketed back up – usually rapidly. This is because their metabolism had slowed down and even small increases in caloric intake caused rapid weight gain.
So to summarize, weight loss can still occur in many people if very low calorie diets are adhered to. However this is not recommended as very low calorie diets are inadequate in nutrients and will make weight regain likely once the low cal diet is discontinued. The best way to lose weight is a moderate reduced calorie diet and regular weight training and cardio.
To answer your second question – I can not tell you exactly how low you can go with your calories before your metabolism will start to slow. This really depends upon your age, weight, activity level and your own metabolism. But I can tell you that you should not consume fewer calories than your BMR (basal metabolic rate). Check out this link to find out your BMR.
Hope this answered your question Daz and thanks for reading CGB!
Martha, thankyou for your websight, you seem to understand much better than the experts I have read. Your answer to Dax is true for me. I have had hypothyroidism for 17yrs & have reduced my calorie intake so as not to put on weight. At present to maintain my current weight I can eat only 500 calories/day – my health is now being effected and i realize that i am not getting the nutrients i need in my diet. My question is – what can i do to now boost my need for calories so i may eat more and get the nutrient intake required?
The style of writing is quite familiar . Have you written guest posts for other bloggers?
Hello;
I’ve lost over 2 stones pretty quickly through excersising, sometimes three hours rowing or three hours walking, or less, and eating a lot less, sometimes less than I’d like e.g. 400 calories. On a day where I’m hungry I’ll eat 800 calories. That fills me up to be honest. I want to be able to eat better and still lose weight, but never at the expense of gaining any weight back- I’d still like to achieve another stone loss, that would be nice. If I ate normally and continued excersigin, would it all just become muscle, make me bigger, or would it help with weight loss…?
So…any tips?
Congrats on your weight loss! You are doing quite a bit of exercise … and eating minimal calories. I’m suprised that you have the high energy levels that you obviously have to work out so much! As you know, calories from food are what fuel your body.
Your low caloric intake and rapid weight loss will likely have an effect of slowing your metabolism. I would recommend that you slowly increase your calories – to a minimum of 1200 …. then even more. I don’t know the exact amount you should consume as I don’t know your age, height or weight. But 1200 would be an improvement. Make sure you are consuming adequate protein as well (at least 70 grams a day). This will help to slow loss of muscle mass. Losing muscle isn’t good as that will slow your metabolism even more.
Good luck!
thank you for your help! Yes, I have slowly been eating more, albeit unintentionally! The problem with 400 cals was I felt fine, but I did get ver faint whenever I stood up, and I began to get very irrational/emotional, which could’ve been something to do with the low calories. I assume so, because now I’m eating more I feel happier =]
I eat a lot of yoghurt, so hopefully that counts towards protein. Many thanks!
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