Off the bat, I should say that I’m actually a fan of eating less. I’m on record as saying that my goal is to figure out how few calories I can eat and still thrive. Still, eating less isn’t always the magic bullet people will hope it will be. There are many ways that eating less can go wrong.
For weight loss, the advice to “eat less, exercise more” often doesn’t work like it “should” on paper. The weight-loss diet industry thrives on repeat customers who struggle to lose weight and keep it off. Dutifully following this strategy has led many people down the road to frustration and dejection, as they blame themselves for their failure to successfully lose weight despite their best efforts to “just eat less.”
From a health perspective, eating less is a double-edged sword. On the one hand, caloric restriction may promote longevity. It certainly does in many animal models. Human evidence is still mixed, but I’m betting that the same is true for us.1 On the other hand, long-term or severe calorie restriction can cause serious health problems, including nutrient deficiencies, hormonal imbalances, and muscle loss.
Today I’m going to look at some of the ways that restricting calories can go wrong—or simply be ineffective—as well as ways to eat less to actually promote health.
Just Eating Less Is (Often) Not Sufficient for (Long Term) Weight Loss
Don’t get me wrong. At the end of the day, if you’re trying to lose weight, the body must expend more energy than it takes in. I’m not talking here about the oversimplified CICO—calories in versus calories out—approach to weight loss. Calories are just one variable in the incredibly complex equation that ends in weight loss. I’m talking about more valid but harder to quantify balance between energy consumed and energy expended.
In both cases, the idea behind eating less is to put fewer calories (or less energy) into the system. However, the energy balance approach recognizes that:
The types and amount of food we eat, as well as when we eat, affect how the body uses those calories.
The “energy out” side of the equation is dynamic. It, too, is affected by the foods we eat, their hormonal impacts, and the body’s natural desire for homeostasis.
Oftentimes, when someone is struggling to lose weight, they’ll get, “You’re just eating too much. Eat less, and you’ll start losing.” This person might already be down to 1100 or 1200 calories per day. They’re thinking, “How can I possibly eat less and still have the energy to get through my day?” The advice-giver doesn’t understand how the body adapts to calorie restriction.
The Body is Incredibly Adaptive
One of the reasons that weight loss is so difficult is that your body actively fights back against it. It makes sense if you think about it. The body stores fat for times of famine. It doesn’t know (or care) if it has stored “too much” according to your personal preferences. When you intentionally try to lose weight, your body “defends” its body weight by altering the amount of energy it expends.2 It tries to tightly ration body fat in case you’re facing a prolonged food shortage.
It does this by manipulating the “energy out” side of the energy balance equation, which comprises several factors:
Basal metabolic rate – the energy your body expends in the everyday functions of being alive (breathing, circulation, generating new cells, etc.)3
Thermic effect of food – the energy it takes to metabolize the food you eat
Activity-induced energy expenditure – the energy you spend moving your body
When you eat in a caloric deficit and start to lose weight, the body responds by lowering its metabolic rate. That’s actually desirable from an aging perspective. Reduced metabolic activity and subsequent lower oxidative stress might explain why caloric restriction promotes longevity.4 It’s not so great when it comes to weight loss.
Moreover, the body responds to caloric restriction by dialing back activity. “Non-exercise activity thermogenesis,” or NEAT, is the term for the energy you expend through spontaneous movements like tapping your feet or nodding your head along to music. NEAT can vary up to 2000 calories per day between individuals.5 That’s a massive difference in “energy out.” It gives your body a lot of wiggle room when it comes to reducing energy expenditure.
These metabolic adaptations aren’t inherently bad. One reason your metabolic rate goes down as you lose weight is simply that smaller bodies expend less energy. Unfortunately, though, it’s also a coordinated attempt to thwart your ongoing weight loss efforts. This is why weight loss is so tricky. There are things happening under the hood that you can’t monitor. Eating less can actually increase your body’s adaptive response, making it harder and harder to lose weight.
People Are Bad at Counting Calories
Another reason the advice to “just eat less” fails dieters is because people are notoriously bad at judging how much they actually eat. In studies, participants chronically underreport their caloric intake, even when they are paid to be accurate6 and when they are dieticians.7
If you’re also trying to balance your food intake against estimates of how many calories you burn through exercise, fuggedaboutit. One study found that individuals believed they burned three times more calories than they actually did on a treadmill test.8 Another small study showed that individuals who were struggling to lose weight underreported their caloric intake by 47 percent and overestimated energy expended by 51 percent, on average.9 (It’s not you. Activity trackers are notoriously terrible at accurately estimating calorie burn.10)
Even if you’re diligently weighing and tracking your food, you’ll probably be off through no fault of your own. The FDA allows a margin of error of up to 20 percent for calories reported on food labels.11 Packaged meals and restaurant meals often contain many more calories than stated on labels and menus. 1213
“Weight Loss” Isn’t Actually the Goal
What you really want is fat loss. Nobody is striving to lose lean muscle or organ tissue or bone mass. Unfortunately, that’s often exactly what happens when people restrict calories too much and for too long without taking great care with what they are eating.
There are lots of ways to eat less. You can start your day low-fat, “heart healthy” (eye roll) cereal and skim milk, drink a smoothie for lunch, and have plain chicken breast and steamed broccoli for dinner. Or, you can eat in a compressed eating window, enjoying eggs, chicken thighs, steak, fatty fish, and abundant vegetables. Only one of these options will get you sufficient protein, healthy fats, and lots of vitamins, minerals, and phytonutrients to mitigate non-fat loss.
When Eating Less Backfires
When It Causes Excessive Hunger
Not surprisingly, hunger is a common complaint among people who are trying to restrict calories. Besides being unpleasant, excessive hunger can derail your efforts by causing you to unintentionally eat more. You take a slightly bigger portion, grab a handful of nuts in between meals, and eventually devour the ice cream hidden in the freezer. Those calories add up.
Some hunger is to be expected if you are eating in a caloric deficit (although there are ways to attenuate hunger that I’ll discuss later). Excessive hunger is a problem, and a sign that you’re overdoing it.
When It Messes with Hormone Balance
Leptin is one of the hormones responsible for regulating appetite. It’s considered an energy indicator, communicating to the brain whether you have sufficient energy on board. When you’re losing weight—specifically when body fat is on the decline—leptin drops.14 In fact, it drops more than would be predicted by body composition alone.15 It seems to be signaling to the brain, “Hey, we’re losing our fat stores over here! Send help.” If leptin gets too low, all hell can break loose. Symptoms of low leptin include hunger, depression,16 loss of libido, and infertility.17
Going too low on calories can also depress thyroid function. In particular, lower T3 seems to be related to calorie restriction even without weight loss. I’m not convinced this is necessarily a bad thing. It may actually be adaptive—another pathway by which caloric restriction increases longevity.18 That said, you can definitely have too much of a good thing. You don’t want to restrict calories to the point where you start experiencing symptoms of hypothyroid such as feeling cold all the time, unexplained weight gain, or fatigue.
When It’s Stressful
I’ve said it a million times: stress is the enemy of health and weight loss. As with so many things in life, calorie restriction can be an adaptive (hormetic) or maladaptive stressor. It all depends on how it’s applied and how your body reacts.
Restricting calories increases cortisol, aka “the stress hormone.”19 Chronically high cortisol leads to problems including:
I know, this sounds like a good thing. If you’re trying to eat less, isn’t it better if your appetite is reduced? Yes… to a point. Anecdotally, I see a subset of people whose appetites are suppressed when they restrict calories—possibly due to being in ketosis20—and who subsequently struggle to eat enough. If they aren’t mindful, they can easily under-eat to the point they aren’t getting enough nutrients.
If you suspect you might be under-eating, use an app like Cronometer to track your food for a few days. Make sure you are checking the nutritional boxes you need to stay healthy.21
When You Burn Muscle Too
Caloric restriction can lead to your body catabolizing muscle tissue if you’re not careful. Some muscle breakdown is probably unavoidable, especially if you are losing substantial amounts of weight, but you want to mitigate it as much as possible. Protein intake is key. Eating more protein protects lean mass (muscle and organs), even when you’re in a caloric deficit and losing weight.2223
When you eat less, make sure you aren’t cutting your protein precipitously. You may even want to increase it a bit.24 Your calorie deficit should come from reducing fat and/or carbs, depending on your current diet.
What about Metabolic Damage?
Dieting forums are filled with dire warnings against dieting so long or so hard that you go into “starvation mode” and create permanent “metabolic damage.”
You might be familiar with the highly publicized Biggest Loser study, which followed contestants from the televised weight loss competition.25 The researchers found that six years after losing significant weight, the contestants’ resting metabolic rate was on average 500 calories lower than would be predicted based on their size. That meant they had to eat many fewer calories (and/or burn more) just to maintain their weight, compared to people with similar body compositions who hadn’t lost a bunch of weight. In fact, many of them regained significant weight in the six years after the show ended.
As I said above, it’s well established that the body defends against weight loss by slowing metabolic rate and reducing energy expenditure. Other studies have shown that this metabolic adaptation persists even when people maintain or start to regain weight.262728
Whether this constitutes permanent metabolic damage is a hotly debated topic. In one recent paper I found interesting, researchers used different equations to analyze old data, taking into account participants’ body composition.29 They concluded that given enough time, metabolism will revert back to pre-weight-loss levels. Even the men from the most extreme weight loss experiment to date, Ancel Keys’s Minnesota starvation study, recovered eventually.
I’m not convinced that caloric restriction “breaks” your metabolism by any means. Still, if you engage in sustained caloric restriction and weight loss, there will likely be a period in which your metabolic rate is reduced. That means if you go right back to eating as much as you were before, you’ll regain weight. It seems to the trade-off.
How To Eat Less and Thrive More
Focus on Nutrients
The less you eat, the more every bite counts. Make the most of the calories you eat by prioritizing nutrient density and getting sufficient protein. Although I embrace fat in my diet, it’s the cherry on top, not the main course. I fill my plate with nutrient-dense meat, seafood, and poultry; eggs; and abundant veggies. Then I add sauces, dressings, and condiments (Primal Kitchen, naturally) for flavor and interest.
Prioritizing nutrient-dense foods ensures that you are being nourished on a cellular level. Consuming mostly low-protein, low-fat, low-nutrient foods will leave you hungry, unsatisfied, and craving more. There’s a reason that physique athletes only follow the “chicken breast and steamed broccoli” diet for short periods before competitions. It’s miserable. It messes with sleep, sex drive, and mood. You’re hungry all the time. That’s no way to live.
Eating sufficient protein increases satiety.30 It helps keep your metabolic rate up by protecting energy-guzzling muscles and organs. Protein also has a higher thermic effect than fat or carbs, further contributing to metabolic rate.31
Cycle Your Caloric Deficit
If you’re chronically in a caloric deficit, say 15 to 20 percent or more, you may benefit from cycling in periods where you eat at maintenance calories. That means you try to eat about the same number of calories you need to break even each day. Obviously you can’t know exactly how much energy you’re expending, but you can use an online calculator to get a rough estimate. It doesn’t matter if you’re spot on.
The idea here is to “reset” your hormones, especially leptin and thyroid hormones. This will also bring your metabolic rate back toward baseline, although it will decrease again once you go back to a caloric deficit.
There’s also something to be said for taking a mental break from restricting calories. Especially if you feel stressed, or you simply get tired of feeling hungry, loosening the reins periodically is a good idea. Stress counteracts the benefits of any diet or lifestyle intervention, including calorie restriction.
There are many ways to execute cyclical dieting. Go with whatever style works best for you. A popular method is 8 to 10 weeks of caloric deficit followed by 2 weeks at maintenance, and repeat. A word of caution, though: Those maintenance weeks aren’t meant to be free-for-alls. Sure, you can enjoy some foods you avoid during the deficit phase. It’s no big deal if you eat somewhat above maintenance some days. Eating 10,000 calories in a weekend can quickly wipe out a few weeks’ worth of caloric deficit, though. If you’re trying to lose weight, you’ll be taking three steps forward, and two (or three!) steps back if you do this. If you’re going for longevity and general health benefits, it doesn’t make sense to binge on inflammatory foods.
Experiment with a Ketogenic Diet
As I mentioned, ketones are known to suppress appetite, which can lead to a spontaneous reduction in calories. If you are struggling with hunger but still eating a moderate- or high-carb diet, consider doing a Keto Reset. Drop your carbs to 50 grams or less. Increase your fat proportionately. (Carbs have 4 calories per gram, while fat has 9 calories per gram. If you reduce your carb intake by 50 grams, that’s 200 calories—about 22 grams of fat.)
Anecdotally, lots of people report that they find it much easier to sustain a caloric deficit on keto. They no longer feel like they are white-knuckling it and relying on willpower. If you have questions about going keto, head to my keto diet hub and grab my free Beginner’s Guide to Keto.
Try Intermittent Fasting
Many people find it easier to eat less when they observe a shorter eating window. Start slowly. If you currently eat between 8 a.m. and 8 p.m.—a 12-hour window—see if you can shorten it by an hour or two. Six- and eight-hour windows are common, but there are no hard and fast rules about what’s optimal. As with keto, intermittent fasting isn’t for everyone, and you have to make sure you’re eating enough in your window.
If you’re eating less for longevity purposes, fasting may give you an extra boost in the autophagy department.
Be Patient, and Listen to Your Body
Although caloric restriction has benefits, it’s a means to an end. Like carb restriction, intermittent or extended fasting, or HIIT, it’s a tool in your metabolic toolbox. Use it appropriately, enjoy the benefits. Apply it too much or in the wrong situations, and you risk digging yourself into a hole. Hopefully, it goes without saying that arying to starve yourself into rapid weight loss is a bad idea. A modest caloric deficit with periodic breaks seems best in most cases.
As always, you should experiment and see what works for you. Especially when it comes to longevity, we don’t have enough solid evidence from human studies to lay out a specific calorie restriction protocol that is optimal. We probably never will given the tremendous variability between people.
Be patient. Stack the odds in your favor by eating satiating, nutritious foods, and by doing all the “other stuff” that supports metabolic health—getting plenty of sleep and sun, exercising appropriately, moderating stress. Resist the temptation to double down on restriction when your body needs a break. Control the variables you can control and make peace with the outcome.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.