“It’s simple,” a friend of mine used to say, “if you want to lose weight, eat less.” Is it that simple? If I had a dollar for every time someone I know went on a 1,500 calorie diet and ended up back where they started or worse 6 months later, I would be rich— but I would still write this newsletter. 

The reality is weight is much more complex than “calories in, calories out,” and that’s a good thing. Read on to understand why dramatic calorie restriction almost always fails and what you should do instead.

Our bodies are smarter than we are

Every day, our bodies are in a continuous process of receiving energy from food and using it to stay alive. It’s true that when we have more energy than we need we store it, and when we have less energy than we need we tap into that storage. 

But here’s the catch: our bodies are brilliant survivalists. We are physiologically hardwired by evolution to protect against too much weight loss (which would lead to weakness and death) as well as too much weight gain (which would make it easier for predators to catch us). 

When we eat fewer calories than we need, our bodies don’t just continue on as if nothing has changed. Everything has changed! Our bodies adapt to less energy coming in by reducing the amount of energy going out. 

This process is called metabolic adaptation and it happens quickly in most people, within a couple of weeks. You can think of this like your body going into “low battery mode.” Once this occurs and your metabolism is reset to a slower rate, it becomes harder to lose weight and easier to gain it.  

How metabolic adaptation occurs

Unless you are a hummingbird in a wing-flapping contest, the majority of your daily energy is not used during your workout. 

Most of our energy (50-70%) is devoted to our Basal Metabolic Rate (BMR). This is the energy required to keep our lungs breathing and our hearts beating – in other words, to keep us alive. When we eat less than we burn, BMR automatically slows to conserve energy (this would be like installing LED bulbs in the house to conserve electricity).

Metabolic adaptation also occurs through a subconscious reduction in “non-exercise activity thermogenesis” (NEAT). NEAT is all the activity you do outside of intentional exercise. If you are fidgeting while reading this, congratulations, you are burning energy through NEAT. There is a huge range of possible NEAT expenditure: it can be near-zero or can exceed 500 calories/day.

In studies of calorie restriction diets, a dramatic reduction in NEAT happens almost immediately after restriction starts. People who used to fidget constantly are suddenly still (the opposite happens when we overeat: NEAT is spontaneously increased). Isn’t the body incredible?

When the diet is over

Many studies have demonstrated that metabolic adaptation can persist long after calorie restriction is stopped. Participants from the TV show ‘The Biggest Loser,’ for example, were studied 5 years after the show’s extreme diet had ended. Despite gaining back most of the weight, participants’ metabolisms were burning 500-700 calories less than they were before the show started.

Evolutionarily this makes sense: the body is incredibly sensitive to the risk of starvation, so it stays prepared for future famines even if the current one has ended. 

This phenomenon helps to explain why many dieters plateau and then gain weight back:

What you should do about it

Does this mean it’s impossible to lose weight? Not at all. Here are three science-based strategies to lose fat and, more importantly, to improve your health without tanking your metabolism.

Keep calorie deficits small

Witty banter should be fast, but sustainable weight loss will be slow. Most people need an energy deficit to lose weight; keeping the deficit small (think 100-200 calories/day) will minimize metabolic adaptation and prevent hormone imbalance, injury, and illness, which are more likely with large calorie deficits.

One of the easiest ways to create an energy deficit is to eat real (whole, unprocessed) food, especially plants:

Keep insulin low

Insulin’s job is to create fat, not to burn it. When insulin is high, it can be very hard to lose weight (think of it like trying to drive when the parking brake is on). To keep insulin low you have to keep your blood sugar steady:

• Minimize or eliminate added sugar (yes, even the artisanal honey), processed food, and starches (bread, rice, pasta)

• Reduce carbs and combine them with protein, healthy fats, and fiber

• Walk after meals

Build lean muscle

For health (and aesthetics), weight is much less important than body composition (the proportion of muscle versus fat and where that fat is located).

Increasing the amount of lean muscle you have will increase BMR and reduce metabolic adaptation:

• Strength train: In addition to building muscle, strength training improves insulin sensitivity and satiety signaling, which promote fat loss.

• Eat enough protein: Current research suggests you should target ~1g of protein per pound of optimal body weight; if your healthy weight is 150 lbs, you should target ~150g/day.

• Consider getting a DEXA Scan to determine your body composition: Companies like BodySpec operate in many big cities and offer scans for $40 to $60. 

Here’s to a week of fine-tuned metabolisms, frequent fidgets, and strong bodies getting stronger. As Einstein said, “Everything should be made as simple as possible, but no simpler.” (If, after reading this, you try a 1,500 calorie diet anyway, please send $1 to my retirement fund.)

Dr. Lauren Kelley-Chew
@drkelleychew

I’m a Stanford and Penn-trained MD and health tech founder with over a decade working on health optimization in Silicon Valley. Biohacking for the Rest of Us is my answer to medical elitism – I want all people to have access to cutting-edge science that can dramatically improve their health.

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