Don't rely on willpower to lose weight: these 2 things will make it easy and sustainable, according to a personal trainer who wrote a book on fat loss

• The personal trainer Ben Carpenter said it's a mistake to rely on willpower to make healthy changes stick.
• For lasting fat loss, Carpenter advises making habits that can be kept long-term.
• Work with, not against, your existing preferences, he said.

If you want to lose weight successfully — and for good — it helps to make it as easy as possible.

By making healthy habits effortless, you won't have to rely on willpower and are more likely to stick to them, Ben Carpenter, a personal trainer and fat loss coach, told Business Insider.

Carpenter's new book, "Fat Loss Habits," is designed to help people set themselves up for sustainable fat loss.

"When it comes to weight loss, a lot of people view obesity traditionally as a lack of willpower," Carpenter said.

But willpower is a finite resource, and at some point, it will run out, he said.

By choosing a form of exercise you enjoy, rather than what's optimal, you're more likely to develop a habit that becomes so ingrained in your routine that you don't have to think about it.

"Over time it becomes second nature," Carpenter said.

Think long-term

Changing your mindset about fat loss could be the key to getting off the yo-yo diet cycle.

Carpenter said that instead of asking yourself how you can lose as much weight as possible as quickly as possible, ask what you could still be doing in a year's time.

"What could you be doing so well a year from now that next January you aren't asking yourself again, 'What diet should I go on?' I think that's a fundamental mindset shift that would help most people," Carpenter said.

People go on and off restrictive diets like they're switching lights on and off, Carpenter said: "If someone can adopt health-promoting behaviors that they can adhere to for long periods of time, arguably the need for dieting diminishes."

For your weight loss to be long-term, you need to think about long-term habits, Carpenter said: "Most people are trying to achieve long-term goals, but they're doing it via short-term behaviors."

Dietitians have previously told BI that diets promising rapid, drastic weight loss are unsustainable and best avoided.

Keep a food diary for a couple days

Carpenter recommends people self-audit before trying to lose weight.

This could be as simple as keeping a food diary for a couple of days to help you identify tweaks. For example, swapping cream in your coffee for milk.

"I prefer to ask people what they're doing at the moment, their own preferences, and then try and find things that take as little effort and cause as little pain as possible," Carpenter said.

He added: "If you can get better results doing 99% of everything you are already doing, it takes a lot less effort and willpower than someone going, 'Here is your new diet plan, good luck.'"

Overhauling your diet can seem doable at the start but motivation often dwindles.

"From a motivation perspective, it could be really exciting to make substantial changes to your eating and watch the scale drop quickly. It might even motivate you to keep going," registered dietitian Alix Turoff previously told BI. "But when your plan is very rigid, this motivation typically lasts only a few weeks before you're burnt out and wanting to quit."