Why am I gaining weight on 800 calorie diet?

Quick Answer

There are a few reasons why you may be gaining weight on an 800 calorie diet:

  • Your calorie intake is higher than 800 calories per day – many people underestimate how many calories they are actually consuming.
  • Your metabolism has slowed down significantly in response to the very low calorie intake, so your body is holding onto fat.
  • You are not eating enough protein, so you are losing muscle mass as well as fat.
  • You are experiencing metabolic adaptation – your body has adapted to the low calorie intake and is very efficient at conserving energy.
  • You have an underlying medical condition that is impacting your ability to lose weight, such as hypothyroidism.

Calorie Intake May Be Higher Than 800 Calories

One of the most common reasons why people struggle to lose weight on a very low calorie diet is that they underestimate their actual calorie intake. Studies show that people tend to under-report their food intake by up to 45% when self-reporting what they eat. Even when you think you are carefully tracking and restricting calories, you may be taking in more than you realize.

Some reasons for underestimating calorie intake include:

  • Forgetting to track snacks or small bites of food
  • Not accurately measuring portion sizes
  • Eating more on weekends or special occasions
  • Drinking high calorie beverages like juice, soda, coffee drinks
  • Cooking oils and spreads added during cooking
  • Restaurant meals tend to have more calories than we realize

To get a true assessment of your calorie intake, it may help to have a nutritionist review a food diary over a typical week. You may find your actual calories are closer to 1000-1200 calories per day rather than 800. Even a small increase of 200-400 calories per day could lead to weight maintenance rather than weight loss over time. Carefully tracking calories for a period can help determine if underestimating intake is the issue.

Tips to Improve Calorie Tracking Accuracy

If it seems your calorie intake is higher than you estimated, here are some tips to improve tracking accuracy:

  • Use a food scale to weigh portions
  • Measure oils, dressings, spreads, nut butters before adding to food
  • Track every snack and taste of food
  • Use a calorie counting app to look foods up as you eat them
  • Stick to mostly whole, minimally processed foods to make tracking easier
  • Plan meals and log calories ahead of time to prevent underestimating

Getting as close as possible to your true calorie intake will help troubleshoot a weight loss plateau on a low calorie diet.

Metabolism Has Slowed Considerably

Severely restricting calories can cause your metabolism to slow down much more than expected, which can hinder weight loss. Your body adapts to food restriction by decreasing the number of calories burned at rest and during activity.

When calorie intake is very low, the body conserves energy by:

  • Decreasing thyroid hormone production – thyroid hormones help regulate metabolic rate.
  • Lowering levels of leptin – this hormone increases metabolism in response to overeating.
  • Increasing ghrelin – this hunger hormone slows metabolism to conserve energy.
  • Reducing NEAT (non-exercise activity thermogenesis) – this includes fidgeting, pacing, standing.

Studies of participants on very low calorie diets (500-800 calories per day) show that their metabolic rate slows much more than expected based on weight loss alone. This means your body is very efficient at conserving calories when intake is severely restricted over a prolonged period. This can lead to a weight loss plateau.

In one study, participants on a 10-week 800 calorie diet experienced a metabolic adaptation that was 29% greater than expected based on their fat and muscle loss. Their bodies had became extremely efficient at conserving energy, making ongoing weight loss very difficult.

Reversing the metabolic slowdown can help get weight loss back on track.

How to Rev Up a Slowed Metabolism

Here are some tips to revive your metabolism after a period of very low calorie dieting:

  • Gradually increase calorie intake to a moderate deficit of 500-750 calories below maintenance level
  • Replace refined carbs with nutrient-dense, fiber-rich complex carbs
  • Incorporate metabolism-boosting foods like chilies, garlic, green tea
  • Start or increase resistance training to build muscle and rev up resting metabolism
  • Add short bursts of cardio intervals to workouts
  • Get adequate sleep and manage stress levels
  • Consider taking a thyroid support supplement if thyroid issues are suspected

As metabolic rate increases again, you should see weight loss pick back up if you maintain a moderate daily calorie deficit.

Lack of Protein Intake

Consuming very little protein is another potential reason for weight loss plateauing on a low calorie diet. Protein intake is critical for maintaining lean muscle mass as you lose weight.

When protein intake is inadequate, the body will break down more muscle for energy as fat stores decrease. Losing muscle mass slows your resting metabolic rate. Since muscle burns more calories than fat, having less muscle means your body needs fewer calories to function, making weight loss more difficult.

How much protein is recommended on a low calorie diet? Experts suggest at least 0.7-1 gram of protein per pound of body weight. For a 150 pound person, that equates to 105-150 grams of protein daily.

Some signs that inadequate protein may be an issue include:

  • Fatigue, muscle weakness
  • Hair loss, brittle nails
  • Muscle soreness, cramps
  • Trouble building/maintaining muscle

To optimize protein intake, include a quality protein source at each meal like Greek yogurt, eggs, lean meats, beans or nuts. Whey and plant protein powders can also help augment protein.

Incorporating More Protein

Here are tips for increasing protein within an 800 calorie limit:

  • Have Greek yogurt with berries for breakfast
  • Add eggs or egg whites to meals and snacks
  • Choose lean meats like chicken, turkey, fish
  • Eat more plant protein like beans, edamame, tofu
  • Snack on nuts, nut butters, or protein shakes
  • Substitute cauliflower rice or zucchini noodles for grains

Consuming adequate high quality protein while cutting calories can help retain muscle and support weight loss.

Metabolic Adaptation

Metabolic adaptation or adaptive thermogenesis also contributes to weight loss plateaus when calories are restricted for an extended period. This occurs as the body strives to maintain homeostasis and survives with less energy intake.

Your metabolism controls the balance between calories consumed and calories burned. During weight loss, your body resists the new lower weight by adaptating metabolically to conserve energy. The greater the calorie restriction, the more metabolically efficient the body becomes at using calories ingested.

Thismeans your body learns how to function on fewer calories than predicted. You have to keep reducing calories just to keep losing weight, which is not feasible or healthy long-term.

In addition to lowering metabolic rate, here are some other adjustments your body makes when you diet:

  • Lowers body temperature
  • Burns less calories digesting food (dietary thermogenesis)
  • Increases fat storage enzymes
  • Increases appetite hormones like ghrelin

These adaptations persist even after weight loss stops, making it harder to lose more weight without further reducing calories. This stalled weight loss can discourage dieters and cause them to give up.

However, there are ways to help overcome the adaptive thermogenesis plateau.

Strategies to Overcome Metabolic Adaptation

Some effective strategies include:

  • Taking periodic diet breaks – increase calories to maintenance for 1-2 weeks
  • Changing up calorie intake and macronutrients regularly
  • Incorporating refeed days with more calories/carbs
  • Lifting weights to build muscle and boost metabolism
  • Doing HIIT and interval training to spur calorie burn
  • Getting adequate sleep and managing stress

Making these changes provides a metabolic reset to help restart weight loss. Patience and persistence are needed to overcome the body’s innate drive to adapt and maintain homeostasis.

Underlying Medical Condition

In some cases, an undiagnosed medical condition could be hindering your ability to lose weight on a very low calorie diet. These include:

  • Hypothyroidism – Low thyroid hormone causes metabolic slowdown and fatigue.
  • PCOS – This hormonal imbalance disrupts metabolism and appetite regulation.
  • Cushing’s syndrome – Excess cortisol drives up insulin and promotes fat storage.
  • Polycystic liver disease – Cysts on the liver impact hormone production and metabolism.
  • Insulin resistance – Cells resist insulin, increasing blood sugars and fat storage.

If you have been struggling to lose weight despite following an 800 calorie diet, speak to your doctor about getting testing done for these or other conditions. Treating the underlying cause could help get your weight loss efforts back on track.

Some symptoms that could indicate a metabolic or hormonal condition:

  • Constant hunger and cravings
  • Fatigue, weakness
  • Inability to tolerate cold
  • Hair thinning or loss
  • Mood changes, depression

Getting any health issues properly diagnosed so they can be managed is key to overcoming stubborn weight loss plateaus.

Other Factors That May Impact Weight Loss

A few other factors that can stall weight loss on an 800 calorie diet include:

  • Sleep – Lack of sleep disrupts hormone regulation of appetite and metabolism.
  • Dehydration – Not drinking enough water can cause water retention.
  • Bowel issues – Constipation and digestive problems can cause bloating.
  • Medications – Some medications like steroids, antidepressants may increase weight.
  • Too little dietary fat – Very low fat diets disrupt hormone function.

Ensuring you get 7-9 hours of quality sleep, drink enough water, have regular bowel movements, and take any necessary medications as directed can all help support your weight loss efforts.

If you are tracking calories closely and not losing weight as expected on a very low calorie diet, have patience and persist. Try the strategies in this article to overcome common weight loss plateau causes. Adjusting your approach can help get you losing weight steadily again.

Example Daily 800 Calorie Diet Meal Plan

Here is an example of what an 800 calorie day might look like:

Meal Foods Calories
Breakfast 1 egg + 2 egg whites scrambled with 1/2 cup spinach, 1/2 grapefruit 134
Snack 1 part-skim mozzarella cheese stick, 10 almonds 104
Lunch Tuna salad made with 1 can tuna, 1 tbsp light mayo, mustard, celery on lettuce 120
Snack 1 apple with 1 tbsp natural peanut butter 100
Dinner 85g (3oz) chicken breast cooked in 1 tsp olive oil with 1 cup roasted broccoli and cauliflower 232
Snack Sugar free jell-o cup 10
Total 800

This meal plan provides a balanced macro split of 40% protein (100g), 35% carbs (70g), and 25% fat (22g). The high protein preserves lean mass, while moderate carbs support energy for exercise. Healthy fats enhance satiety and help optimize hormones.


Plateaus and stalled weight loss are common hurdles when following an 800 calorie diet. Carefully reviewing your calorie tracking accuracy, optimizing macros, addressing metabolic adaptations, and ruling out medical issues can help get the scale moving downwards again. Adjusting your diet and exercise plan to push through a plateau is key to long-term weight loss success. With patience and troubleshooting, an 800 calorie diet can be sustainable and effective for reaching your goals.

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