With the turn of the New Year often comes resolutions about losing weight –  often in the 1 500-reasons from of killing calories going forward. And if that’s really what you want, there’s nothing wrong with that—as long as you approach weight loss with a healthy mindset and healthy habits. To oversimplify it, weight loss does require burning more calories than you consume. But is 1 500 calories a day enough to sustain your energy levels—and power you through rides?

Some weight loss plans suggest men should consume 1 500 to 1 800 calories each day and women consume 1,200 to 1,500 calories each day to shed pounds safely. Meanwhile, according to the current Dietary Guidelines for Americans, those assigned female at birth and aged 19 through 30 require about 1 800 to 2 400 calories a day, while those assigned male and of this age need about 2 400 to 3 000 a day. For those ages 31 through 59, most females require about 1 600 to 2 200 calories a day and males about 2 200 to 3 000 calories a day.

What’s more: The more active you are, the more calories you need. And as cyclists, we burn a significant amount of calories each day we ride (more so than many other forms of exercise), so severely restricting our calorie intake can actually do more harm than good. Here’s what you need to know about having 1,500 calories a day.

Is 1 500 calories a day really enough?

As mentioned, the short answer is probably not. Fifteen hundred calories sounds like a lot when you think about it in terms of exercise. If a 70kg rider burns around 540 calories in an hour riding at 12 miles per hour on average, it would take almost three hours of exercise to burn those 1 500 calories. And it’s not uncommon for a weekend long ride to hit the three-hour mark. Plus, exercise isn’t the only way we burn calories.

“It’s likely that most adults have a basal metabolic rate (BMR) close to, if not higher than, 1 500 calories per day (depending on age, body weight, and height),” says Allison Knott, R.D.N., a New York City-based specialist in sports dietetics. Your BMR (a.k.a. metabolism) is the amount of energy your body needs to run properly and keep you alive—before you factor in daily physical activity or exercise. “Knowing this, it’s easy to see why 1 500 calories wouldn’t meet the needs of most active adults or athletes,” she adds.

When you’re active, you need even more calories to support your energy needs on top of your BMR. And not meeting the basic energy requirements for the body to function properly not only compromises your normal bodily processes like digestion, it makes riding efficiently a whole lot harder, if not impossible.

Not eating enough calories also ups your risk of missing out on essential nutrients. “This includes adequate macronutrient intakes of carbohydrate, fat, and protein as well as micronutrient intakes of essential vitamins and minerals,” says Knot. Consuming the right types of calories is so important because you don’t just need carbs for short-term energy, but you also need healthy fats and protein for endurance, recovery, and to feel satiated.

What happens when you restrict calories?

Athletes aren’t immune to the idea that the less calories you consume, the lighter and leaner you’ll be—and the better you might perform (especially when you’re trying to be aerodynamic or float uphill on a bike). But the key word there is might. Restricting calories may make you lighter, but it may also make you a more tired, weaker, and injury-prone athlete.

When you’re under-fuelled, your body can actually go into starvation mode. If you don’t have enough accessible energy (i.e., calories), “the body will shift to slowing the metabolism down, and saving energy by increasing your body fat stores,” explains Rebecca McConville, R.D., a sports nutrition specialist and author of Finding Your Sweet Spot in Sport: How to Avoid RED-S. “At some point, the body halts allowing body fat for fuel and shifts to using muscle.”

That’s right: Cutting calories too much can actually cause you to lose muscle mass. If you’re not eating enough calories post-exercise, that can mess with muscle protein synthesis, says Knott. And if you don’t have enough available energy (especially if you’re not eating enough protein), your body will actually start breaking down your muscle for energy. “Both of these underscore the importance of adequate calorie intake not only to allow muscles to recover and build after training, but also to prevent loss of existing muscle mass,” Knott says.

Besides that, you can see energy imbalance manifest throughout the whole body. “Digestion will start to slow, making you feel fuller quicker; enzyme production slows in your GI system and you can become more intolerant to particular foods; your body temperature drops making you colder; for women, your menstrual cycle will start to dysfunction and eventually shut off, and for men, testosterone drops, causing them to have less libido and less facial hair,” explains McConville.

You can also see shifts in mood and sleep cycle, and you might experience fatigue, exhaustion, poor sleep, difficulty concentrating, increased risk of injury, slower recovery time, and an increased risk of illness, adds Knott.

What’s worse is that these negative effects don’t just disappear when you resume eating more calories. They can have a long-term impact on your internal systems.

How does a 1 500-calorie diet affect performance?

Obviously, losing muscle would be detrimental to your power on the bike—and probably directly contradicts your training and fitness goals. But it goes so much deeper than that.

“If a cyclist doesn’t consume adequate calories to meet his or her needs, then it can have a cascading effect where performance during training is reduced due to the poor energy availability,” says Knott. “Muscle protein synthesis is impaired post­-training, which results in reduced training adaptations, and glycogen stores aren’t replenished, which results in reduced energy availability during the next training session.”

Plus, you’ll have to work harder to see the same effects as your rate of perceived exertion declines. “You’ll slowly lose your endurance ability, which means you’ll hit a wall sooner,” says McConville. “And since your energy stores have been used up on basic energy needs, you won’t have as much to help with recovery, leaving you a more tired, sore athlete.”

What’s a better way to lose weight?

Weight loss shouldn’t be just about crunching calorie numbers. As mentioned, you do have to consider calories in versus calories out, but it’s not quite that simple. The quality of those calories matters. Weight loss is so individualised and depends on a variety of factors, including body size, age, gender, fitness level, training schedule, stress, environment, medication, and other chronic health conditions if present, Knott says.

Making smaller changes such as cutting out alcohol, replacing highly-processed carbs with whole grain carbs when appropriate (think: off the bike), or cutting back on refined sugars in favour of fruit are all simple swaps you can make that will increase your health without decreasing your performance. Having your body composition tested is another option to figure out your personal needs.

That said, it is common for endurance athletes to consume a minimum of 2 500 calories, and some may need as much as 5,000 calories, says McConville. “The Journal of the International Society of Sports Nutrition recommends caloric intakes ranging from 25 calories per kilogram bodyweight for an active, healthy individual to 80 calories per kilogram body weight for an elite athlete,” says Knott.

But if you are concerned about the numbers, a healthy amount of weight loss for the average person is a little over half a kilo per week, or about two to three kilos per month, according to the Centers for Disease Control. That translates to a calorie deficit of 500 calories a day. Which means, if you’re starting out at 2 500 calories to keep up with your endurance needs, you should only be going as low as 2 000. Or if you’re an active man starting at 3 000 or an active woman starting at 2 400, you’d only drop as low as 2 500 or 1 900 respectively.

“It’s always good to work with a registered dietitian who specialises in sports nutrition if you’re planning to start a new training regime or to participate in an endurance event or other sports event requiring specialised training and nutrition,” says Knott.

Just remember that calories aren’t everything. Focus instead on the composition and quality of the calories you’re consuming, and eating what makes you feel best when you’re on the bike—and off of it.

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