Even Gunnar Peterson, L.A.’s celebrity trainer to the likes of Jennifer Lopez, Khloe Kardashian and the Lakers, has witnessed some holiday-related slacking off among those in his inner circle. Just like many of us, they began blowing off their workouts and overindulging the weekend before Thanksgiving. “A few have been terrible since that Friday, and that then rolls into Christmas and the New Year,” said Peterson.

“People miss a workout, and then they can’t control the rest of the downward spiral,” he said.

No argument here. But how to change that?

While most of the people who work out with Peterson are focused and motivated, he concedes that that is not a realistic reflection of society at large. Many people loathe exercise, many more try it and give up, said Peterson, who is currently filming the reality series “Revenge Body with Khloe Kardashian,” and recently partnered with Irvine-based MitoQ, a biotech company that has launched an antioxidant supplement. (It is one of two supplements he takes daily, the other being a multi-vitamin, and says that “while there is no magic pill, this one helps your cells function more efficiently.”)

The good news, though, is that Peterson says you don’t need to hire a sought-after celebrity trainer to get in shape and drop bad habits. Here, he offers some tips on how to reverse that downward spiral — and sustain a new health and fitness regimen once you start it.

1. The flat-tire analogy

Everybody is aware of the pitfalls of overindulging. I’m not going to be the guy who says, “Don’t go to any parties, go to bed.” That’s not reasonable. People want to indulge and they should. Just don’t let all the wheels come off. Don’t miss your training, eat badly, get drunk and not sleep. If you lose one wheel, you can still limp along. All four wheels come off? You’re done.

2. It’s OK to hate exercise

A lot of the time, it’s fear of the unknown. Just put your toe in the water and build up to it. Your first workout doesn’t have to be a run. Consider your injury history. Ask yourself how much time you can really allot to this, and how much of the rest of your life will be geared toward fitness and well-being. I have a client who works out, and then he’ll drink tequila and beer. In his mind, he’s doing what he can do, and that is better than nothing.

3. There will be a turning point

Someone will say, “You look good.” Or you go on vacation and look better in your bathing suit than before. Maybe you notice your energy is up or you have fewer sick days. You connect the dots and think, “Maybe working out has been helping.”

4. Try it all

I don’t ever want your association with fitness to be bad. I want it to be fun, maybe even great. But that might take a bit. I’m all for “fitness dating” — try yoga, spinning, strength training, hiking. Then find what you can fit in your schedule, and what you enjoy. You’re way more likely to be consistent with it. And if you’re consistent with it, it will work for you.

5. Fitness is free

People can’t claim not to know what to do. There are 50 million articles on fitness. I’m not going to say it’s easy to be in shape because it requires effort. But it’s easy to know what you have to do. You don’t have to go beyond the pay walls. Instagram is free and full of fitness professionals. Find something you like. If you are de-conditioned and haven’t worked out in a year and you see a guy pushing a sled 50 yards and then dropping down into a burpee and doing jumping jacks, that’s too much. So dial it back until you can say, “I like this person’s approach. I like how they speak. I can process it.”