For almost a decade, I lived in a New York City high-rise apartment building with a small, well-stocked gym in the basement. While walking on the treadmill or doing my own strength-training sessions, I frequently watched my neighbors power through sweat-inducing workouts with personal trainers coaching them at their sides.

In such a small space, it was impossible not to overhear their conversations. I’d listen to cues meant to help the exerciser perfect their form and tips on how long to rest between sets — guidance you’d expect a fitness pro to give their clients. But to my surprise, many of the coaches also doled out nutrition and diet advice, most of which hadn’t been backed by science or was dangerously restrictive.

As a registered dietitian, I found it really hard to keep my mouth shut when I’d hear those conversations. And nowadays, I see plenty of personal trainers and “fitfluencers” promote the same problematic tips and nutrition plans on social media. Each one of these posts tempts my colleagues and me to drop a face-palm emoji in the comment section.

I may sound like a cranky R.D. with a “get-off-my-lawn” attitude, but by and large, personal trainers and fitness coaches shouldn’t be advising their clients on their eating habits and nutrition. Of course, there are exceptions; some trainers have obtained extensive nutrition science education, for example, and can give sound advice on foods to support exercise performance and recovery. But before you take your trainer’s nutrition and diet advice at face value, you should keep these points — and major red flags — in mind.

How Nutrition Can Benefit Exercise

Before diving into who can — and shouldn’t — provide nutrition guidance, you need to know why your eating habits and food choices matter when it comes to your fitness. Put simply, nutrition can complement an exercise plan and help you achieve specific fitness-related goals, whether you’re training for a race, trying to build muscle, or working towards healthy weight loss or weight gain. For example, fueling properly before a workout with the right balance of carbohydrates (a macronutrient that provides energy) and protein (a macronutrient essential for supporting muscle growth) can help promote exercise performance. And you’ll need to score both of those nutrients after your workout to replenish your glycogen (a form of glucose, which is derived from carbs) stores, repair muscle, and overall support post-exercise recovery.

But these best practices aren’t something you typically learn in your high school health class. In turn, some folks may seek out nutrition tips to support their fitness journeys from their personal trainers. Or, the coaches themselves may share their own hot takes without being asked — even if they don’t have the education or training to back them up.

What Nutrition Advice Can Personal Trainers Provide?

To be clear, trainers can talk about food. But it’s important to consider if the information they’re sharing is within their scope of practice. It’s similar to how doctors, dietitians, and therapists can mention research on the mental and physical health benefits of exercise, but they may not have the credentials necessary to give their patients or clients a detailed workout plan.

The American Council on Exercise (ACE), for example, shares specific guidelines on what nutrition topics fitness professionals can generally discuss. This includes dietary advice provided by the federal government, such as those found in the Dietary Guidelines for Americans and the MyPlate recommendations. Additionally, folks who’ve passed fitness certification programs accredited by the National Commission for Certifying Agencies or American National Standards Institute can provide basic nutrition information, according to ACE. To the organization, this “basic” info includes principles of healthy eating and food preparation; the essential nutrients, their role in the body, and how to incorporate them into your diet; how nutritional needs change throughout your life; and the nutritional content of foods and supplements.

Aside from those fundamentals, there are certain instances in which trainers may provide more specific nutrition advice, including if they’re also registered dietitians. These individuals have completed the necessary core nutrition science education (think: courses on organic chemistry, biochemistry, food science and production, clinical nutrition, nutrition and metabolism through the life cycle, and more) and six to 12 months of supervised training to pass a nationally recognized licensing exam. They’ll also need to have a four-year degree (and as of 2024, a Master’s degree) to take an exam that certifies them to legally practice as a dietitian. All things considered, registered dietitians have a nuanced understanding of nutrition that personal trainers simply can’t offer.

You may also feel comfortable seeking out or receiving nutrition advice from trainers who have credentials from comprehensive nutrition programs geared toward personal trainers. Look for certifications from Precision Nutrition (e.g. PN-1 or PN-2), the Institute for Integrative Nutrition, the Nutritional Coaching Institute, and the National Academy of Sports Medicine’s Nutrition Coach program.

Just know that these certification programs don’t entail the same degree of nutrition education as registered dietitian programs, so if you have an underlying condition or concerns that require more nuance, you may still wish to work with a dietitian. For example, if you have diabetes or prediabetes and need to be mindful of blood sugar, consider working with an R.D. They’ll have a better understanding of the condition and can explain what may need to be different for you in terms of meal timings, carbohydrate portions, and exercise, especially if you are using medications to manage your blood sugar. Or if you’re pregnant, you’ll want to work with someone who understands how your nutrient needs change throughout each trimester.

When You Shouldn’t Take Nutrition Advice From a Personal Trainer

Remember: Unless your trainer has a nutrition certification from an accredited, well-recognized program, proceed with caution if you’re taking specific diet advice from them. Generally speaking, fitness pros shouldn’t provide individualized nutrition recommendations or meal planning; assess your nutritional needs and recommend specific calorie, nutrient, or dietary intakes; counsel you on how to prevent, treat, or cure a disease; or prescribe nutritional supplements, according to ACE. If your trainer or coach makes any of these suggestions, take it as a red flag.

If your trainer recommends any of the following — regardless of their certifications — they’re not a good source of nutrition information.

They suggest cutting out entire food groups.

From a mental and physical health standpoint, removing entire food groups from your diet is a slippery slope. Aside from potentially missing out on essential nutrients that support performance and recovery, avoiding specific food groups can set up an overly restrictive mindset and may potentially contribute to disordered eating habits.

I often overheard trainers in my apartment’s gym telling their clients to restrict dairy. But interestingly, milk, Greek yogurt, kefir, and cottage cheese offer up a great combo of easily digestible carbs and protein — nutrients essential for daily living and workout recovery. If you don’t feel well when you eat dairy, then cool, don’t eat it. But if you tolerate it and it serves you, feel free to keep it on your plate or in your glass.

Keep in mind that a trainer who tells you to swear off dairy or cut out all carbs may be coming at you from their own place of fear around these foods. Or, they may have simply received their nutrition education from some viral TikTok post, not a legitimate institution.

They encourage extremely restrictive or very low-calorie meal plans.

Aside from making the act of eating incredibly boring, restricting your diet ups your risk of missing out on key nutrients and potentially harms your gut health. For example, consuming adequate amounts and different types of fiber is important for supporting gut health, and eating a variety of foods can help you cover more bases to support your microbiome’s optimal function. If you’re eating the same few foods over and over again, however, you could be missing out. Plus, not consuming enough calories can make it difficult for the body to perform and recover from exercise.

Restricting your diet to an extreme can also breed an unhealthy “on plan/off plan” mentality; you might find yourself eating very differently when you’re not following your (usually very restrictive) meal plan, often overindulging in foods that aren’t included in that plan. This all-or-nothing pattern can make it incredibly challenging to meet your nutrition goals and sustain any results you do see.

You should also be skeptical if your coach is overly specific about which brands are “good enough” to include in your diet. For example, I once overheard a trainer tell someone to avoid all carbs — except Ezekiel bread. While I love sprouted-grain bread, which is rich in fiber and protein, it doesn’t have to be your only source of complex carbs.

They try to sell you supplements.

Remember: Fitness professionals shouldn’t supply, prescribe, or sell nutritional supplements to clients, according to ACE. Though supplements are sometimes considered less “serious” than medications, you still need to be careful about potential interactions with other medications you may be taking and quality control issues, as the supplement industry isn’t regulated as heavily by the U.S. Food and Drug Administration as drugs and medications are.

A few thoughtfully chosen supplements (such as those you determine to be beneficial with the help of an R.D., doctor, or other qualified professional) may be used for addressing a specific health concern. But if a trainer is pushing large amounts and you feel pressured to purchase things when you don’t even really know what they do, take a step back.

They label foods as ‘good’ or ‘bad.’

If your trainer refers to specific foods as either “good” or “bad” or makes you feel judged for your eating habits, break off the relationship. Even if you feel like you’re more likely to stay on track if you’re getting your ass kicked (yes, I’ve heard this from patients and clients before), hearing someone else’s voice berating your food choices can lead to a build-up of negative self-talk, potentially damaging your relationship with your body and your relationship with food. You want to work with a qualified professional who will meet you where you are — not shame you — and come up with an individualized program that takes your goals, needs, and preferences into consideration.

The Bottom Line

In most cases, personal trainers should provide you only with basic nutrition information, so take any other guidance with a grain of salt — or as a sign to start working with someone new. However, if your coach has done additional nutrition training to support their exercise recommendations, it may be okay to take their advice — just remember to trust your gut. And if you have more specific nutrition needs or just want a reality check, consult with a registered dietitian.

FTR, this works the other way too; I wouldn’t ever encourage someone to get an exercise plan from a dietitian or doctor who wasn’t a trained instructor. Different health experts have different areas of expertise, so scope out their credentials and choose to work with someone who makes you feel empowered, supported, and safe.


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