Eating only 400 calories a day is a very low calorie diet and would likely lead to significant weight loss. However, it is not a sustainable or healthy way to lose weight. Such a low calorie intake can cause fatigue, irritability, and weakness.
Key Takeaway: Burning 400 calories a day can help you lose around 0.8 lbs per week. However, you may lose more or less than this depending on things like your starting body weight, body fat percentage, your gender, and how old you are.
Eating at a deficit of 400 calories is considered a healthy and sustainable deficit to get you to your weight loss goal. If you're consistent with a 400-calorie deficit, you can expect to lose around 0.5-1 lb per week. Creating a 400-calorie deficit can be as simple as reducing your portions at each main meal.
No matter what type of diet you follow, to lose weight you need to burn more calories than you take in each day. For most people with overweight, cutting about 500 calories a day is a good place to start. If you can eat 500 fewer calories every day, you should lose about a pound (450 g) a week.
On the 'fasting' days, it is recommended you consume less than 25% of your recommended daily energy intake, roughly 400 calories.
Chance of nutritional deficiencies
Eating 500–800 calories a day may put people at risk of deficiencies. Specific groups of people may be at higher risk. Older adults, in particular, may be at risk as they are more like to have reduced nutrient absorption from the small intestine.
If you're not losing weight in a calorie deficit you may need to adjust your stress levels, diet, and sleep patterns. Other reasons for weight gain during a calorie deficit are hormonal changes, aging, and other health conditions.
If you can eat 500 fewer calories every day, you should lose about a pound (450 g) a week. Always talk with your health care provider to determine a healthy weight for you before starting a weight-loss diet.
There are 7,700kcals (kcal=calorie) worth of energy in 1kg of fat. That means in order to burn 1kg of fat, you must have a calorie deficit of 7,700.
In addition, consuming as few as 800 calories daily may not give you the energy you need for daily living and regular physical activity, especially if you eat the same foods every day. Talk to your doctor or dietitian to make sure you get the nutrients you need while on a very low-calorie diet.
Summary: A daily 400-calorie deficit will lead to a 2,800-calorie weekly deficit, helping you lose around 3.5 pounds monthly. However, your gender, age, training intensity, and activity levels can influence your results.
Eating only 400 calories per day would be considered an extremely low-calorie diet and could have serious consequences for your health. At such a low calorie intake, your body would not be getting enough nutrients to function properly. You would likely feel fatigued, weak, and experience difficulty concentrating.
To lose one pound of weight per week, you should consume approximately 1,500 calories per day. Active women who walk for over 3 miles per day need to consume at least 2,200 calories to maintain their weight. To lose one pound of weight per week, you should consume approximately 1,700 calories per day.
For weight maintenance, the Dietary Guidelines for Americans 2020–2025 suggest a range of 1,600–2,400 calories for women and 2,200–3,000 for men — so you could consider anything below these numbers a low-calorie diet.
However, other studies show that while consuming 1,000 calories a day may result in significant weight loss, most people cannot sustain it and often experience significant weight regain . The reasons include regaining lost muscle mass and increased appetite. Also worth noting is that the human body can adapt.
If 1,200 calories a day is more than 500 calories lower than your weight-maintenance calories, you can expect to lose more than 1 to 2 pounds per week.
So, if you're eating 1,200 calories and not losing weight, it could be that your body is really struggling to function on so little fuel and your metabolism is not functioning well enough to respond to a deficit in the way you'd like.
When you cut your food intake to 1000 calories and below, your body is forced to break down muscle so that it can provide your body with energy since your food intake does not provide it with enough energy. This results in a person losing their muscle and affects their metabolism as we've just highlighted above.
Not for long, unless you are obese. And I don't mean that as in you think you are obese. You cannot survive on 500 calories per day for long unless a medical professional has examined you, measured you, weighed you, and told you you are obese.
For a weight of 100 to 120 lbs, if you eat 500 calories per day, you will lose 2 to 3 pound per week. Warning at this weight 500 calories a day is probably too much of a calories restriction for you. Follow the link above to use the daily calorie calculator to a get a personalized calorie per day recommendation.
To lose about 0.5kg a week, you would need to consume 500 calories below your daily calorie requirements. To lose 0.25kg a week, you would need to consume 250 calories below your daily calorie requirements.
You will suffer malnutrition and disease, perhaps be at risk of sudden death. Extended starvation, which a 600-calorie diet is, is serious. I'm sure you've heard of the RDA, the recommended daily allowance of all the nutrients I mentioned that the medical professionals believe is absolutely necessary to stay healthy.