NASM Certified Trainer, Ben Crane, explains the pros and cons of relying solely on diet to achieve weight loss. 

To the young lady who posed this question to me, thank you very much. I know this is something everyone loves to think about, especially when we’re a few minutes into our workouts and facing the strong temptation to just call it quits for the day…possibly forever. Working out isn’t always fun, especially when our bodies are already out of shape. While finding the right kind of workout for you is another topic for another time, let’s discuss what would happen if you did give in to temptation and tried to get skinny without working out.

Clarifying “Skinny”

First off, I know many love to gripe and complain about the word “skinny”. So let me just say, I’m not advocating for crash diets, poor body image, much less body-shaming when I talk about getting or staying “skinny.” Skinny means something different to everyone, and it doesn’t have to be a bad thing. When I think of skinny, I simply think of someone with a low but healthy body fat percentage, as well as low amounts of muscle mass. Please don’t assume that it means someone with an eating disorder, or that we should all aspire to be skinny. Neither of those things are true, and now that I’ve said my peace, let’s move on.

When it comes to our body weight, aside from our natural growth until we reach our peak height, everything becomes determinable by our activities and our nutrition. Since this article is focused on being inactive, I will focus solely on nutrition.

It’s Science. Not Genetics.

Contrary to what some believe, your body doesn’t magically create body fat. It’s not genetic, and doesn’t appear out of nowhere. Body fat is our natural way of storing excess energy for when we may potentially go without food. I know that sounds crazy because most people who read this are likely surrounded by food, but when you think about how long humans have been on Earth it’s easier to understand why our bodies would need the ability to store energy for times food was scarce. By the way, it is precisely BECAUSE we are flooded by food that the majority of First World adults are overweight, but that also is a topic for another time.

The only way our bodies can get the energy they need to function is by eating and drinking. We have to consume food that contains fats, carbohydrates and protein, all of which are broken down by our bodies to utilize their stored energy for our own survival (alcohol is technically another energy provider, but for obvious reasons not one we should rely on). When we consume more energy than our bodies can use, our bodies store that excess energy in fat cells around the body.

Now I’ll be the first to admit that genetics do play a role in one’s efficiency at both burning and storing body fat, but again we only absorb energy from food. We don’t get energy from our genetics. We don’t get energy from the air we breath. The only energy going into your body is what YOU choose to put in your stomach, so unless you’re a child and someone else is deciding what you eat, the only person you have to blame for the body fat you accumulate is you.

Now that know the simple science behind body fat, we can discuss how to use it to our advantage, which in this case is how to get skinny (burn off excess body fat) without working out.

Diet and Exercise

If body fat only develops from calories we consumed that were in excess to what our body was able to burn, and body fat provides energy to our body when we are short on food, then it makes sense that to begin burning off excess body fat we just need to consume fewer calories than we burn so our bodies will use that stored energy to make up for the deficit. Furthermore, to stay skinny, we just need to keep our daily calorie intake as close as possible to the amount of calories we burn each of those days.

Believe it or not, it’s as simple as that. If we consume fewer calories than we burn, our bodies WILL make up that deficit using energy we have stored within us. Unfortunately, not only is that energy deficit often made up for by burning the wrong type of stored energy (proteins from our muscle tissue), but our metabolism can take a nose-dive, resulting in a much lower daily calorie expenditure. You can imagine that if our metabolism continually slows down, the amount of calories we would have to consume to stay in a deficit would be so small we’d be stuck starving all day, and we would be robbing ourselves of vital nutrients that our body needs daily because it’s unable to store them (amino acids from protein being one of many of them).


Our bodies are unable to store excess protein, so it’s one of the many nutrients we need daily. When we consume more protein than we can use, it either gets converted into glucose that we can use for immediate energy (if we’re not getting glucose from carbohydrates), or it’s converted into body fat to supply energy later. While many factors can lead to this, if we don’t feed our bodies the necessary amount of protein they need they will eventually react as if they can no longer sustain the amount of muscle they have, break down our muscle tissue, and extract the amino acids from those proteins for energy use or other cellular development.

To maintain or increase muscle mass, we have to consume adequate amounts of protein, as well as prevent our bodies from taking the metabolic nose-dive into starvation mode.

Starvation Mode

Everybody’s metabolism is different, but most metabolic fluctuations can be attributed to the common laws of metabolic science. As discussed previously, our bodies are great at storing excess energy we consume for use at a later time. However, not only are they great at storing energy, but they’re great at conserving it as well. To conserve energy, our bodies will actually lower our metabolic rate, reducing the amount of calories we burn, which is great when we’re legitimately going through starvation, but terrible when we’re trying to drop as much body fat as possible. “Starvation Mode” is really just a phrase people tend to throw around to refer to our bodies reaction to various stimuli that result in a loss of muscle mass, decrease in metabolic rate, and inability to shed body fat.

Get Skinny

Now that you’ve learned what it takes to burn our bodies’ fat stores, as well as how our bodies may respond, you might be thinking “this makes it sound like our bodies were made to get fat and stay fat”. That’s most definitely not true. While getting fat is easier than it has ever been before (America especially), the science behind losing and maintaining weight is well established and understood, and with the right plan of action it can be a lot easier than you might think to lose weight. It can also be very enjoyable, which is where a personal trainer comes in very handy because they can incorporate activities you enjoy doing into a workout that targets fat burning, builds muscle, boosts your metabolism and leaves you feeling accomplished, proud and excited to come back and do it again and again.

What I’m trying to make you see is that by not ‘working out’, you’re really backing yourself into a corner that is very hard to come out of. Lack of physical activity leads to muscle atrophy, higher stress levels, lower sleep quality, all of which contribute to a lower metabolic rate. But if you really want to lose weight without working out, you’re going to have to follow a highly restrictive diet plan, one which only a licensed nutritionist should create for you. It’s going to require adequate amounts of protein every day, as well as systematic cycling of high and low calorie days to prevent your body from going into starvation mode. This will help preserve muscle mass (although without exercise you will likely experience some muscle atrophy) and keep you in a calorie deficit most days but factor in some higher calorie days to help keep your metabolism up.

As a fitness professional, I can’t stress the value of regular physical activity enough, but at least this should educate you on the basic science of metabolic dieting. If you have any feedback, questions or suggestions for future posts, please leave those in the comments below!