When you sit down to indulge in your grandmother's tasty fried chicken, your traditional Thanksgiving gorge fest, or the fast-food meal you picked up because you didn’t have time to make something, you might think to yourself, "How much can this one meal really hurt my health?" Although moderation that includes occasional treats is an important component of a healthy relationship with food, you might not like the answer to this question.
Several studies have shown that just one meal has extreme power to negatively affect your health. The upside? It is not just unhealthy meals that have the power to make significant changes in just one go. Studies also show that even in a short period of time, a healthy diet can positively impact your health.
Knowledge is power, as they say. Recognizing how one meal affects your overall health can help you determine just how to incorporate treats and moderation into your diet without sacrificing the many gains your overall healthy diet and lifestyle provide. Plus, there are a few things you can do to mitigate the effects, as long as you recognize they do not give you free reign to always indulge.
The Effects of a Single High-Fat, Poor-Quality Meal
There are several negative effects on your body that occur in the hours after consuming a single, high-fat meal, defined as one with at least half the calories from fat, mostly saturated fat. For one, it increases your risk of heart disease. Endothelial (the inner lining of blood vessels) function is an early marker for atherosclerosis (a disease of the arteries) risk, and consuming a high-fat diet impairs endothelial function. In one study, participants consumed an Egg McMuffin®, Sausage McMuffin®, two hash browns, and a non-caffeinated beverage from McDonald's. The meal makeup was 50 g fat, 14 g of saturated fat, 255 mg of cholesterol, and a total of 900 calories. The control group consumed a low-fat meal with the same number of calories but 0 g of fat and 13 mg of cholesterol consisting of Kellogg's Frosted Flakes®, skim milk, and orange juice.
In the group consuming the high-fat meal, flow-dependent vasoactivity (which affects blood vessels and how much they relax or contract), a marker for endothelial function, decreased from 21 (+/- 5%) to 11 (+/- 4%) two hours after consuming a high-fat meal. Lower levels of flow-dependent vasoactivity correlate with endothelial dysfunction, and the changes increase the risk of damage that may lead to atherosclerosis. The low-fat meal had no affect on the endothelial function. There was an inverse correlation with fasting LDL cholesterol levels and the flow-mediated vasoactivity before the meal. Changes to the flow-dependent vasoactivity also inversely correlated with changes in serum triglycerides. This means a high-fat meal at least temporarily alters the endothelial function, which can promote the formation of fatty plaques in the arteries and could be one way fat and cholesterol increase the risk of developing atherosclerosis.
A single meal also could increase the risk of developing hypertension (high blood pressure). A study using a randomized, crossover design looked at the effects of consuming a high-fat meal on cardiovascular reactivity to a stressful task on individuals with normal blood pressure. The participants either consumed a high-fat breakfast from McDonald's (a Sausage McMuffin®, an Egg McMuffin®, and two hash brown patties). Alternatively, the participants consumed a low-fat breakfast consisting of a bowl of Kellogg's Frosted Flakes®, skim milk, fat-free yogurt, a Kellogg's Fruit Loops® fruit bar, and Sunny Delight® orange juice. The two meals had the same calories and sodium levels, thanks to an additional sodium supplement to the low-fat meal. The participants underwent four stress tasks: mental arithmetic, public speaking, arm ischemia, and cold pressor. Their blood pressure was taken at baseline and during the tasks.
After consuming the high-fat meal, the participants had an increased reactivity to the stress, although it did not affect their blood pressure at baseline. Although the exact changes differed by task, there was a pattern of increased reactivity in those who had the high-fat diet. This type of exaggerated response to stress is associated with a higher risk of developing hypertension.
Consuming a single high-fat meal also leads to increased fat in the liver, which is linked to insulin resistance, metabolic diseases, and non-alcoholic fatty liver disease. In a crossover study, the nine participants consumed a meal consisting of sausage rolls made up of 61.5 percent fat, 31.6 percent carbohydrates, and 6.9 percent protein that totaled half their daily recommended calories. To compare the effects of the meal with additional protein, the subjects consumed a protein powder in addition to the meal to bring the protein content up to 20 percent at a different time. Using H-MRS, the researchers were able to assess the fat content of the liver after the meal. There was an increase in the intrahepatic lipid, or fat levels in the liver, during the first three hours, and remained even five hours post-meal. There was no difference in the fat content in the muscular tissue, and the added protein did not make any difference in the storage of fat in the liver.
Another study found that one-time binge eating could increase the risk of insulin resistance. It looked at the consequences of binge eating by having participants consume a high-fat diet of 68 percent fat that was 78 percent higher in calories than necessary to parallel the typical high-fat, high-calorie meals on which people binge. The participants had individual diet plans, but a sample diet included pork sausages, bacon, fried eggs, fried white bread, and whole milk for breakfast. A sample lunch consisted of white bread, butter, cheddar cheese, mayonnaise, and a sausage roll. A sample snack included a pork pie. A sample dinner was beef burgers, bacon, cheddar cheese, and coleslaw, followed by dessert of a chocolate chip muffin and double cream. After eating a normal diet for seven days, the subjects consumed the experimental diet on the eighth day. It was a small study with just 15 subjects, but it found a reduction in insulin sensitivity by 28 percent after the single high-fat, high-calorie meal. This result signals a shift toward insulin resistance after just a one-day binge.
A high-fat meal might also contribute to oxidative stress and inflammation. In one study, consuming a high-fat, high-carbohydrate meal with excess calories for lunch for four days led to an increase in oxidative stress. In this study, the test group consumed a Burger King Double Whopper® burger with regular French fries, a small Coke®, and regular onion rings that was made up of 173 g carbohydrates, 93 g fat, and 65 g protein. All participants followed a meal plan for seven days adhering to the dietary reference intake for Koreans. Then the group divided into those eating the above lunch for four days and a control group continuing the standard diet. The average consumption per day for the control group was 2,600 calories, 340 g of carbohydrates, 66 g of fat, and 120 g of protein, while the high-fat group consumed 3,500 calories, 410 g carbohydrates, 130 g fat, and 130 g protein.
In the group consuming the high-fat lunch, there were higher levels of ROS and ONOO-, which are free radicals that contribute to oxidative stress, in the blood samples. These levels did not change on the control diets. Many antioxidant enzymes were released by the body to protect against these increases. Although the antioxidant enzymes could handle an initial increase in oxidative stress, continuing to consume the high-fat, high-calorie meals led to increased markers of lipid peroxidation (a process by which free radicals “steal” electrons from the fats in cell membranes, which can result in cell damage) in a short time. This finding indicates that in a short period of time, the body exhausts its ability to bounce back, so to speak. In other words, although you might be able to handle the increased oxidation of one meal, you will quickly exhaust your resources if you keep eating this way.
While this study did not discuss this point specifically, one might suggest that if your body is already under oxidative stress, the impact of a single, high-fat meal might be even bigger as your antioxidant reserves are already taxed.
The effects of a single meal might be greater in those who are overweight or obese. One study compared 23 men of normal weight and 23 men considered overweight or obese. Participants were randomly assigned to either a group consuming a high-carbohydrate meal (89 percent) with no fat for one to two weeks followed by a meal with 45 percent carbohydrates and 25 percent from fat or a group that consumed the same high-carbohydrate, fat-free meal for one to two weeks and then consumed a high-fat meal with 4 percent carbohydrates and 96 percent fat. For this study, the meals were different versions of a special nutrition shake that were either high-carbohydrate, normal carbohydrate, or high-fat.
The overweight and obese men had higher blood glucose levels after consuming the high-carbohydrate meal than the normal-weight men. Both groups also had a higher blood glucose (i.e., sugar) response after the high-carbohydrate meal than the normal carbohydrate meal, as well as higher insulin levels. In the overweight and obese men, triglycerides also rose to high levels after the normal carbohydrate and high-fat meals, despite the men having normal triglyceride levels prior to the study and the meal using mostly unsaturated fatty acids. Thus, not only do the meal components determine the metabolic response after a meal, but the body composition and energy balance do as well.
What this evidence tells us is that after a high-fat meal, especially one that is also high-calorie and not nutrient dense, the following might occur, particularly in those who are overweight or obese:
- Reduced insulin sensitivity that increases the risk of insulin resistance
- Decreased endothelial function, increasing the risk of atherosclerosis
- Increased serum triglycerides, especially saturated fats
- Increased fat in the liver, which increases the risk of fatty liver disease, insulin resistance, and metabolic disorder
- Increased oxidative stress and inflammation
- Increased metabolic endotoxemia and subsequent inflammation
- Increased cardiovascular reactivity to stress, which could lead to hypertension
Now, if you consume a healthy diet most of the time and are generally healthy, then you might be able to handle an occasional, rare indulgence and bounce back without much of an issue. However, when these indulgences begin to happen more often, you face an increased risk of these post-meal changes developing into the associated chronic health conditions, such as diabetes and heart disease.
The Short-Term Effects of Healthy Meals
The good news is that healthy diets also have the power to significantly affect the body quickly. This time for good. In contrast to a high-saturated fatty acid meal, consuming a healthier mixture of fats does not have the same impact on the body. In one study, 28 healthy males randomly consumed either a high-saturated fatty acid meal or a Mediterranean-type meal. While the meal high in saturated fats led to dysfunction after the meal, including abnormally high insulin concentrations in the blood and higher lipid parameters, especially in those with a higher BMI, the Mediterranean-style diet did not. Additionally, the plasma fatty acid profiles of those who consumed the saturated fat meal were enriched saturated fatty acids while the Mediterranean-type meal led to omega-3 fatty acids rich fatty acid profiles.
Another study found that consuming a Mediterranean-style diet for just 10 days improved cardiovascular function and mood. In a crossover study with 24 healthy women participants, the women either consumed their normal diet for 10 days and then switched to a Mediterranean-style diet or consumed the Mediterranean diet for 10 days and then reverted to their normal diet. There were significant improvements in blood pressure measurements. There were also significant positive changes to cognitive function, including word recall.
Studies on other healthy diets, such as the Paleolithic diet, macrobiotic diet, and vegetarian diet, also demonstrate that consuming them for a short period of time leads to healthier biomarkers.
Ways to Reduce the Damage
There are ways to blunt the damage that one meal does to your body. Of course, this does not mean you want to go crazy with your diet. However, it does provide tools for your arsenal so those days you choose to indulge will not have quite as extensive an impact on your health as they could.
Fish Oil
If you are looking for another reason to ensure you have adequate levels of omega-3 fatty acids, supplementing with them can help reduce the negative impact of food. In a randomized crossover study, researchers had participants supplement for 4 weeks with 4 g per day of omega-3 fatty acids (1.9 g of EPA and 1.5 g of DHA). Some of the participants took the fish oil in the first part of the study while the rest took it in the second round of the study. There was a four-week washout period in between. Unlike the above studies, this study looked at the effects of consuming a cookie that had 75 grams of carbohydrates, 28.5 grams of fat, and 9 grams of protein rather than a high-fat, high-calorie meal. The omega-3 fatty acid supplementation reversed the decrease in %FMD (flow-mediated dilation) after the meal, which is a marker of endothelium-dependent vasodilation. This means it reduced the endothelial dysfunction that correlates with atherosclerosis. It also led to a significant reduction in triglycerides levels.
Antioxidants
Having a good antioxidant capacity, which can be done by consuming antioxidants, helps mitigate the oxidative stress caused by a high-fat meal. A study looked the effects of dietary antioxidants consumed with a high-fat meal. In a randomized crossover study, 25 healthy subjects consumed either a high-fat meal, a high-fat meal with dietary antioxidants from vegetables, or a high-carbohydrate meal with similar calories. The high-fat meal led to an increase in triglycerides, and the antioxidants slightly mitigated that rise. The researchers also performed an l-arginine test to determine a change in blood pressure and platelet aggregation. The high-fat meal led to no change in blood pressure from the vascular response or platelet aggregation. Consuming the antioxidants partially restored these responses, although they were not to the level of the carbohydrate meals.
One study found that taking flavonoid supplements for a period of four weeks reduced the decline in endothelial function. Flavonoids are a type of polyphenol known to have strong antioxidant properties, as well as other beneficial effects on health. In a crossover study on 25 patients, the participants were randomly assigned to taking either a supplement or a placebo, with a two-week washout period. In the placebo groups, there was endothelial function deterioration after consuming a high-fat meal at both baseline and after four weeks. However, taking the flavonoid supplement led to no change between the fasting and after meal values for endothelial dysfunction, although there was one at baseline.
When consuming supplemental forms of antioxidants, the timing might have an impact. In one study, there was a difference in the inflammatory response when consuming vitamin E and C supplements either before breakfast or before supper. Both prevented a rise in CRP, a marker of inflammation, but those consumed before dinner were more effective. Another study supports the idea that pretreating with vitamins C and E could mitigate the endothelial dysfunction.
L-Arginine
In one study using a control group, supplementing with 15 g of l-arginine attenuated the effects of a high-fat meal. In the group taking the l-arginine supplements, there was less of a decrease in the FMD. Although the FMD attenuation still occurred, it was less in those who took the l-arginine supplementation. Most likely, this result is due to a reduction in the oxidative stress caused by the high-fat meal, as well as the requirement of l-arginine to form nitric oxide, one of the mediators of endothelial function.
Walnuts
Adding walnuts to the meal might also make a difference in the effects on the body. In a randomized, crossover trial, 12 healthy subjects and 12 with high cholesterol consumed a high-fat meal with either added olive oil or walnuts. The flow-mediated dilation was worse with the olive oil meal than the walnuts. This effect was independent of changes in oxidative stress, inflammation, or ADMA concentration. Most likely, this result is due to the combination of antioxidants, phytonutrients, l-arginine, and omega-3 fatty acids found in walnuts.
Exercise
Performing exercise before consuming a high-fat, high-fructose meal might help reduce the increase of plasma triglycerides after the meal. In one small study of eight healthy resistance-trained men, performing resistance exercise 15 hours prior to consuming the meal did not alter insulin levels, but it did lead to 16.5 percent and 24.4 percent reduction in the triglycerides in the blood for each of the two exercise groups in the study.
So, if you are going to indulge, make sure that you:
- Have sufficient omega-3 fatty acids
- Consume some colorful fruits and vegetables during the meal to ensure you get plenty of antioxidants
- Consider including foods rich in l-arginine, such as lean meats and/or pumpkin seeds
- Exercise regularly, especially 24 – 48 hours prior to your indulgence
- Limit the number of times a year you indulge!
By recognizing the power of just one meal, you will better be able to judge when it is okay for you to indulge but still maintain the healthy lifestyle you have worked so hard for—and when it is best to stick with your healthy diet instead.
It is important to note that in many of these studies, the food quality was poor and the fat was mostly saturated and/or trans fat. Consuming a meal high in healthy fats that is also nutrient-rich with lots of colorful fruits and vegetables will have a different impact than the high-fat meals common in the processed-food diet, such as something from a fast-food restaurant. Ultimately, it is the quality and quantity of the fat and the other foods on the plate that matters.