The Connection Between a High-Fat Diet, Gut Health and Weight Loss

|Updated Mar 10, 2022
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If you want to maintain a healthy weight, first think of eating for a healthy gut, according to the latest research. A diet high in saturated fat from meat and dairy leads to metabolic conditions, increases the risk of obesity, and makes it harder to lose weight and maintain a healthy weight over time, the study finds. The link between gut health and metabolism is central, the research indicates, and your gut health is compromised when you eat too much fat.

Instead, the science points out, it's important to focus on eating more whole foods such as fruits, vegetables, and healthy complex carbohydrates like legumes and minimally-processed whole grains: You’ll keep your gut microbiome healthier, and be more likely to maintain a healthy weight as a result.

People often eat fat to avoid “carbs,” and ironically this can make it harder to lose weight and keep it off, which is directly related to the state of one's gut health, experts and studies say. Maintaining a healthy gut, research now shows, is critical to keeping us healthy and maintaining a healthy weight. A healthy gut microbiome – the balance of bacteria in our intestines that breaks down food – is even more important to stay healthy and support our immune system, heart health, and nutrient absorption as we age. 

What is the microbiome and why it matters

You’ve probably heard the term microbiome but may not know exactly what it means. A related word, biome, means “major life zone.” For example, think of all the plants and animals within a tropical rainforest or savannah: that is a biome in the natural world. In an analogous way, we play host to our own living things on a micro-level, which is our microbiome.

The microbiome is the collection of all the bacterial organisms, or microbiota, that live on and within us. We are home to trillions of bacteria, as well as viruses, and fungi – some good, some bad – with the largest collection of these living in our intestines. They help break down the food we eat and turn it into fuel for our cells. A healthy gut bacterial balance helps our other cells function optimally, including our circulatory system, immune system and how we use or store fuel. That’s why so much attention is given to our gut microbiome and gut health. 

The role of diet is critical to the intricate and interrelated colonies of gut flora: What we eat determines which of the bacteria and microorganisms flourish and which wither. Our bodies build up delicate gut flora colonies depending on whether we snack on potato chips or crudites, and whenever we put anything into our mouths, we help determine which bacteria thrive and which ones waste away.

Gut microbiome and health connection

Researchers are just starting to understand how important the gut microbiome is to our overall health, but what’s clear is that a delicate balance of good bacteria and bad bacteria affects our overall health A healthy gut is critical to good digestion and strong immunity. It affects our brain health, circulatory system, and hearts. 

Just as in a tropical rainforest or grassland, it makes sense that the healthfulness of the ecosystem is the health of the organisms that live there. It's the same with our gut health. And as with other types of ecosystems, gut diversity is critical to health. 

Choosing to eat mostly whole-food, plant-based diet, with little or no animal fat, helps to feed and grow your gut's “good” bacteria, according to a study in the journal Nature Metabolism, and helps us to live a longer, healthier life. That means eating a diet rich in high-fiber plant foods such as legumes, vegetables, fruits, whole grains, and a limited amount of nuts and seeds, which though they are nutritious whole foods are also high in fat.

Unfortunately, the Standard American Diet, with its focus on processed foods that are high in added sugar and added fat, as well as high in meat, dairy, and unhealthy saturated fat – and lots of it – throws that ecosystem out of balance. 

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The different types of fats

All fat is not equal when it comes to gut health and maintaining a healthy weight. And as with health overall, the type of fat you eat affects your gut health. That means it’s important to understand the types of fat, says Amy Gorin, RD, a plant-based registered dietitian and founder of Master the Media in Stamford, CT. She explains the type of fat to watch for:

  • Monounsaturated fats, or MUFAs (monounsaturated fatty acids), are a type of unsaturated fat. Unsaturated fats are usually from plant foods. A hydrocarbon chain that contains a double bond is unsaturated (more than that are "polyunsaturated" fat). Oils that contain monounsaturated fats are typically liquid at room temperature, but once chilled will tend to turn solid. Olive oil, sesame oil, avocado oil, and peanut butter are foods that contain high concentrations of monosaturated fats. 
  • Polyunsaturated fats, or PUFAs (polyunsaturated fatty acids) have more than one double bond in the molecule. Foods that have high concentrations of these fats include sunflower oil, walnuts, and sunflower seeds. They are liquid at room temperature. Processed vegetable oil, in most of the packaged foods you buy, contain PUFAs.
  • Saturated fats, or SFA (Saturated Fatty Acids), refer to a fatty acid chain with only single bonds between the carbons in the chain, making them stronger and harder, and more solid at room temperature. Saturated fats are primarily found in high concentrations in animal foods such as meat and cheese, though plant foods such as coconut oil and palm oil are also concentrated sources, says Gorin.
  • Trans fats, or TFA (trans fatty acids), are not found in nature. They are created when food companies turn liquid oils into solid fats, and they’re found in processed or snack foods or fried foods. When you see the words “partially hydrogenated oil,” this is a warning it contains trans fat. “You should completely avoid trans fats,” says Gorin. 
  • Combinations of fats. Any food containing fat is often a mix of different types of fats. So even healthy plant-based foods such as olive oil will usually have some amount of saturated fat. Whether it is considered healthy is often a matter of degrees and how much you use.

Even small amounts of dietary fat add up

In a typical day of eating the Standard American Diet, fat calories add up, which can mean your gut microbiome shifts away from healthy and makes it harder to maintain a healthy weight. See how easy it is to overdo it on unhealthy saturated fat in your diet especially if you eat fast food or prepared food at fast-casual restaurants. 

  • Breakfast: Burger King Sausage, Egg, and Cheese Biscuit, 37 grams
  • Lunch: McDonald's Chicken Selects Premium Breast Strips, 40 grams, McDonald’s Medium Fries, 19 grams
  • Coffee break: Starbuck’s Caramel Frappuccino, Grande with Whip, 15 grams
  • Dinner: Cheesecake Factory Fish & Chips, 121 g fat

Total fat for the day: 213 grams.

Even some seemingly "healthier" choices can pack in the dietary fat. For example, take a look at the fat content in these popular fast-casual menu items:

  • Panera Greek Salad without dressing, 34 grams
  • Quiznos Tuna Melt, Regular, 94 grams
  • Baja Fresh Bean and Cheese Burrito, 33 grams

Even plant-based offerings can be high in fat For example, a Beyond Meat burger patty contains 14 grams of fat, 5 of which are saturated, according to the food label. In other words, fat can add up quickly – even if you’re eating a vegan or plant-based diet, though that’s less likely on a whole food plant-based diet.

How much fat should you eat?

According to the Dietary Guidelines for Americans, no more than 10 percent of calories each day should come from saturated fat. “This would be no more than 20 grams for a 2,000-calorie daily diet,” says Gorin.

The American Heart Association and the American Stroke Association suggests an even lower amount for heart health and recommends that fat intake (from all types of fats) should be no more than 35 percent of total calories, though experts throughout the health field recommend that trans fats intake should be zero or as low as possible. 

Saturated fat from meat and dairy should also be avoided, according to Dr. Joel Kahn, a plant-based cardiologist and world-recognized expert on heart health, and author of The Plant-Based Solution, since it leads to hardening of the arteries and heart disease.

The impact of a high-fat diet on gut health

Most of what we hear about fat and health has to do with heart health. For example, monounsaturated fats in modest amounts may be beneficial to cholesterol levels and help to reduce the risk of heart disease. Eating foods containing polyunsaturated fats such as walnuts and sunflower or flaxseeds may help keep cholesterol levels in check, and may help reduce the risk of heart disease and stroke, according to research.

Studies have shown that saturated fat found in meat, dairy and tropical oils such as coconut and palm oil contributes to high cholesterol and can increase risk of heart disease; many leading researchers warn that saturated fat is not healthy and contributes to heart disease.

One study suggested that “reducing saturated fat intake for at least two years causes a potentially important reduction in combined cardiovascular events (by 21 percent).” A number of other studies have shown an association between trans fats consumption and an increase in the ratio of bad cholesterol to good cholesterol and an increased risk of cardiovascular disease. Trans fat is known to wreak havoc on your health in a number of ways.

High-fat diet linked to metabolic conditions

What we eat is critical for a healthy gut in determining the mix and diversity of bacteria in our intestines. A number of studies have linked fat consumption and poor gut health, which leads to metabolic conditions, and difficulty maintaining a healthy weight.

A recent study in the journal Clinical Nutrition found that "high fat and high [saturated fat] SFA diets can exert unfavorable effects on the gut microbiota and are associated with an unhealthy metabolic state," the authors wrote. "Also high MUFA [monounsaturated] diets may negatively affect gut microbiota whereas PUFA [polyunsaturated diets] do not seem to negatively affect the gut microbiota or metabolic health outcomes."

Consuming too much fat over time has negative repercussions on metabolic function, contributing to issues such as insulin resistance, dyslipidemia, and oxidative stress, which is essentially aging on a cellular level. A high-fat diet can contribute to the loss of friendly
"good" gut bacteria, and leads to conditions such as gut barrier dysfunction, also known as "leaky gut," which is essentially leakage of toxic bacterial metabolites into blood circulation.

All of these enable the development of low-grade systemic and chronic inflammation, according to a review in the academic journal Cells. “The high intake of saturated fats, including excessive amounts of omega-6 polyunsaturated fatty acids (PUFA), small amounts of omega-3 PUFA, and an unhealthy omega-6/omega-3 ratio of 20:1 is especially harmful in terms of the metabolic consequences,” write the authors.

Obesity and gut health

A healthy gut, with the right amount and diversity of bacteria, is critical for processing food and extracting nutrition and energy from it. (Your stomach breaks down the food you eat but your gut sorts it and absorbs it into the bloodstream as energy and fuel.) Microbes produce healthy energy from the soluble fiber in the vegetables, fruit, legumes, and plant-based foods that you eat (since there is no fiber in animal products). Your gut helps your body to absorb nutrients from your diet, such as vitamins and minerals, including essential ones like vitamin C, A, E, K and B, including folate, that all help prevent harmful pathogens or viruses from flourishing, neutralize any potential toxins and strengthen the immune system. 

Gut microbes play a critical role in how well our bodies process food and how we use and store energy. Research has established a clear relationship between nutrition, our gut microbiota, and our potential for obesity, according to Nutrition Today. “The bacteria in our gut not only play an important role in digestion, but research indicates that our microbiome could also play a major role in whether or not we become obese,” writes the author. Research has found a relationship between obesity and changes in microbiota composition; reduced bacterial diversity is associated with the propensity for weight gain, for instance. In one study, gut microbiota was used to design customized diets and help subjects lose weight effectively.

That is not to say you should strive for a “no-fat” approach to your diet – since you need some healthy fat for satiety. "Fats help keep you satiated and fuller for longer, which can help reduce your snacking throughout the day,” explains Gorin. “I like to recommend that people include a plant-based source of unsaturated fat—such as pistachios, avocadoes, or olive oil, with every eating occasion.”

Bottom Line: Gut health impacts your weight, your health, and your metabolism.

You need a lot less fat than you are likely eating, even on a plant-based diet, for optimal gut health and to maintain a healthy weight. To create a diverse gut microbiome, stick with a low-fat, plant-based diet and focus on eating mostly fruit, vegetables, legumes, and whole grains.