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Bigger calorie deficits will allow you to lose weight faster, but are you getting the right nutrients? How low can you go, in terms of your daily calorie budget, and still stay healthy?

It must have happened pretty gradually — I didn't pay much attention. Once an XS, I'd gradually become an S, and then an M, and then a L. Each "step up" was a bit annoying, but hey, not all stores use the same sizing systems, right? It wasn't until I started needing an XL, at some places at least, that I started paying attention. 

I'd lazily — meaning, not all that seriously — tried diets before. I didn't enjoy being on them, because I liked food (and still do), and didn't want to participate in a weight loss program that told me exactly what and when to eat, mostly bland, boring, soulless stuff. Then I discovered calorie-tracking apps, and decided that was something I could do. I could still have the kinds of meals I enjoyed. I just needed to slash the quantity, and cut out the mindless snacks (and the beer, of course). 

So, I signed up for an app where you indicate your current weight, BMI, your level of activity, how fast you want to lose weight, and your goal weight. I decided I was going to go with the "middle of the road" option of one pound a week, which equals roughly half a kilo, and that meant a daily calorie deficit of about 500 calories. 

That went great, and I did lose a pound a week on average — sometimes a bit more, sometimes a bit less. I had no trouble making sure I didn't go over my "calorie budget" and actually started eating a much healthier diet, mostly meeting my nutritional targets. That is, until I lost quite a bit of weight and the daily calorie budget dropped and dropped. I was at a healthy weight, but still wanted to lose a bit more. That's where things get blurry.

When the app suggested 1,200 calories, I went with it — but when I started getting recommendations to eat no more than 1,000 calories a day (unless I added physical activity, of course), I started wondering if that was really healthy. Many "losers" who committed to restricted-calorie diets will have this same question. How low can you safely go? How low is too low?

How many calories do you need to eat to stay healthy on a weight loss diet?

Even the National Institutes of Health make the same, fairly common, recommendation that I personally followed: "Follow a healthy diet, and if you are overweight or obese, reduce your daily intake by 500 calories for weight loss." (They also encourage you to move your body regularly, and cut down on the amount of time you're physically inactive, of course.) 

The advice to slash your daily intake to the point that you've got a nice deficit of 500 going on will help you lose weight while still allowing you to eat a healthy diet that meets your nutritional goals (enough vitamins, minerals, proteins, fat, and carbs) if you are currently obese, overweight, or even at the upper end of the healthy weight range. Depending on your current weight, you may also be able to work with a deficit of 700 calories a day and still stay healthy.

As you lose weight, your basal metabolic rate — the calories your body burns just by performing is basic functions, like breathing, digesting what you eat, and making your heart beat — will also go down, however. That means you'll either have to burn more calories through exercise or other physical activity or eat even less if you want to keep losing weight. 

How low can you safely go? If you are extremely obese, your doctor may recommend a medically-supervised very low-calorie diet. These diets, which are especially formulated to give you all the right nutrients, consist of between 450 and 800 calories a day, and are usually only advised for people who are waiting to undergo bariatric surgery, to help them get down to a weight that makes the surgery safer. 

For everyone else, unless your doctor says otherwise after very careful consideration, a diet that low on calories is dangerous. Instead:

  • Men trying to lose weight usually shouldn't go below 1,500 to 1,800 daily calories. 
  • Women shouldn't eat less than 1,200 to 1,500 calories a day. 

Yes, you can lose more weight by going lower, but probably not in a healthy and sustainable way

The rationale behind this is that you don't want to starve yourself, and you don't want to have a daily calorie goal that makes it all but impossible to get the right nutrients without using supplements. People lose weight for all sorts of reasons, but being healthy should certainly be one of the main goals.

You can only stay healthy by eating right. And that means:

  • Eating vegetables of all kinds. According to the Dietary Guidelines for Americans, that means "dark green, red and orange, legumes (beans and peas), starchy, and other". Each kind contains different vitamins and minerals, and offers a source of dietary fiber. (If you're following a 2,000 calorie diet, you should eat a bit more than two cups of veg a day.)
  • Whole fruits of different kinds, which are important sources of nutrients, especially vitamin C and potassium. 
  • Whole grains (limit refined grains). They're especially high in important minerals like iron and zinc, and have B vitamins as well as dietary fiber. 
  • Protein. The source will vary depending on your diet, especially whether you're vegetarian or vegan or a meat eater, but proteins can include poultry, seafood, red meats, eggs, dairy, nuts, and soy products. 
  • You need fat (which includes oils) in your diet as well, particularly monounsaturated and polyunsaturated fats. 

(You don't need added sugar or alcohol — and can obviously safely cut those out! Yup, that'll save you some calories.)

If you are, in line with health recommendations everywhere, pretty physically active and move your body at least 150 minutes a week while doing some kind of muscle-strengthening exercise at least twice a week, you'll have an easier time losing those last few pounds, without dipping below the number of calories you need to stay healthy. 

People whose calorie-counting apps recommend daily calorie intakes of less than 1,500 to 1,200 (depending on their sex) should, however, consider why that might be. You're either not moving nearly enough, and need to add more physical activity to your schedule, or you've already hit a very healthy weight and should consider switching to maintenance. 

Got more questions about safe ways to lose weight? Remember that your doctor knows more about your health and needs than recomemndations designed for entire populations ever could — and if you want advice tailored to you, they're there to help. 

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