How you lose weight matters. If you don’t eat enough, your metabolism switches to slow-mo.
Severe diets, especially when you also exercise, teach your body to make do with fewer calories. That can backfire because your body clings to those calories, which makes it harder to take the weight off.

Strict Diets

Eating too few calories can cause a major decrease in metabolism.
Although a calorie deficit is needed for weight loss, it can be counterproductive for your calorie intake to drop too low. When you dramatically lower your calorie intake, your body senses that food is scarce and lowers the rate at which it burns calories.

Eating too few calories

Eating enough protein is extremely important for achieving and maintaining a healthy weight.
The increase in metabolism that occurs after digestion is called the thermic effect of food. The thermic effect of protein is much higher than that of carbs or fat. Indeed, studies indicate that eating protein temporarily increases metabolism by about 20–30% compared to 5–10% for carbs and 3% or less for fat.
Although metabolic rate inevitably slows during weight loss and continues to be slower during weight maintenance, evidence suggests that higher protein intake can minimize this effect.

Low protein intake

Without enough H2O, your metabolism can stall. 
How about a tall, cool glass of water? Some studies show that it helps the body burn energy and fuels weight loss. At any temperature, water also helps you fill up, so you eat less.
Sip it throughout the day. You also can eat more foods that are naturally rich in water, such as watermelon or cucumbers.

Less water intake

When you are in a stressful situation, your body makes a hormone called cortisol. 
It’s meant to give you a quick boost of energy. But if you’re stuck in a stressed-out zone, the body thinks you still need to fight, so it keeps making cortisol. 
High levels of this hormone make it harder for your body to use insulin. 
That puts the brakes on your metabolism and fuels weight gain.

Chronic Stress

Refined carbohydrates are very different from carbohydrates found in whole grains, fruit, and vegetables.
Don’t reach for refined carbs like white flour and sugar. “Those are quick to digest, meaning your body uses less energy to break them down. The higher-in-fiber whole grains slow down digestion and make your body work harder to break down nutrients"

Eating too many refined carbohydrates

Sleep is extremely important for good health. 
Sleeping fewer hours than you need may increase your risk of a number of illnesses, including heart disease, diabetes, and depression. 
Several studies note that inadequate sleep may also lower your metabolic rate and increase your likelihood of weight gain. 
Lack of sleep is made worse by sleeping during the day instead of at night. This sleep pattern disrupts your body’s circadian rhythms or internal clock.

Not getting enough high-quality sleep

Sugar-sweetened drinks are detrimental to your health.
High consumption is linked to various ailments, including insulin resistance, diabetes, and obesity. Many of the negative effects of sugar-sweetened beverages can be attributed to fructose. 
Table sugar contains 50% fructose, while high-fructose corn syrup packs 55% fructose. Frequently consuming sugar-sweetened beverages may slow down your metabolism.

Drinking sugary beverages

We all know this is the most important meal of the day but with traffic, meetings, and getting kids to school, this meal can suffer.
We might not think of it as a big deal but it greatly affects our bodies, thus our metabolism slows down during sleep. You need to break the metabolic fast to give your body an energy boost

Skipping breakfast

Being sedentary may lead to a significant decrease in the number of calories you burn every day.
Notably, many people have lifestyles that mainly involve sitting at work, which can have negative effects on metabolic rate and overall health.
Although working out or playing sports can have a major impact on the number of calories you burn, even basic physical activity, such as standing up, cleaning, and taking the stairs, can help you burn calories.
This type of activity is referred to as non-exercise activity thermogenesis (NEAT).

Leading a sedentary lifestyle

One glass of wine at night won’t kill you. However, if you’re drinking every night of the week, it can kill your metabolism.
Once alcohol is in your system, it hinders your body’s fat-burning speed and thus burning less fat and slowing down your metabolism. 
If you are trying to boost your metabolism, stick to water and if you do have a drink, try to have heart-healthy red wine instead.

Drinking too often

Working out with weights is a great strategy to keep your metabolism from slowing.
Strength training has been shown to increase metabolic rate in healthy people, as well as those who have heart disease or are overweight or obese. It increases muscle mass, which makes up much of the fat-free mass in your body. 
Having a higher amount of fat-free mass significantly increases the number of calories you burn at rest. Even minimal amounts of strength training appear to boost energy expenditure.

A lack of strength training

12 Bad Health Habits That Kill Your Metabolism| Weight Loss Tips| How to Speed up Your Metabolic Rate|