context: There are plenty of ailments -- such as stomach flu, a migraine, or cold sores --- that can make it temporarily hard to eat or keep food down. But with other, long-term health conditions, those problems often linger. Your appetite may dim. Or you may find it hard to chew or swallow. Or you could have trouble digesting or absorbing the nutrients in food, and then have side effects from poor nutrition. And in some cases, medicines (chemotherapy, for instance) can make you nauseous. There are often ways to get some relief. The first step is to know what's going on and why it's happening. What happens: Over time, uncontrolled diabetes harms your nerves. If it damages your vagus nerve, which stimulates muscles that move food through your digestive system, digestion can slow down or stop. That can lead to heartburn, nausea, bloating, and feeling too full after you've eaten. Doctors call this gastroparesis. The most common cause is diabetes, but it sometimes also affects people with nervous system disorders, like Parkinson's disease (see below) and multiple sclerosis. What helps: The most important thing is to manage your blood sugar, bringing it to the target range your doctor recommends. For the gastroparesis itself, cut down on fatty or high-fiber foods, and carbonated drinks. What happens: People with chronic heart failure can lose muscle mass, as well as fat and bone, leaving them frail. Causes include swelling of the bowel wall, which prevents the absorption of nutrients, and liver or kidney disease that can result from heart failure. They may lead to nausea. Once the wasting process starts, poor nutrition can make it worse. What helps: It can help to eat small meals more often. And it's important to limit salt and fluids in order to avoid swelling and worsening shortness of breath. What happens: The condition itself doesn't affect your gut. But your medicine might. If you take some pain-relieving drugs, such as ibuprofen or naproxen, for too long, that can cause stomach ulcers. Stronger prescription medicines called opioids have constipation as a side effect. What helps: Talk with your doctor about your medicines. And get some exercise. It's good for your joints, as long as you stick with activities that aren't jarring. ( For instance, choose a hike instead of a jog.) Being active helps keep your bathroom habits regular. What happens: The extra weight makes you more likely to have heartburn or GERD (gastroesophageal reflux disease), which is more severe than normal heartburn. If you have weight loss surgery, you'll need to eat less because your stomach is now smaller. Depending on the kind of operation you get, you could need to take supplements, because your body will have less opportunity to pull nutrients out of the foods you eat. What helps: Every step you take toward a healthier weight will bring you closer to relief. If that includes weight loss surgery, talk with your doctor about what nutrients you need, whether you should take supplements, and how to change how much you eat. If you have GERD, tweaking your diet can often make a big difference. Your doctor may suggest you follow a low-fat eating plan, cut out certain foods and drinks (like coffee, chocolate, or tomatoes), and eat small, frequent meals. What happens: Cancer comes in many forms. Both the disease and its treatments can affect your nutrition. Many types dim your appetite, cause stomach pain, or make it tough to absorb the nutrients in food. Other kinds -- such as cancers of the head, neck, and esophagus -- can make it hard to chew and swallow. Then there's nausea from the treatments themselves. What helps: Your doctor may prescribe medications to boost your appetite and help your digestive system work better, or prescribe what's known as ânutrition therapy,â which may range from making changes to your diet to using a feeding tube. What happens: This lung disease gradually makes it harder to breathe. People who have it often find that their appetite isn't what it used to be. People with severe COPD can get very thin because they burn so many calories with the work of breathing. What helps: Since the disease causes your body to use up lots of energy during breathing, it's important to make sure you get enough calories. Make sure you get adequate fats and proteins in your diet and eat small, frequent meals. What happens: The effects of a stroke depend on what part of the brain it affects. Many people who've had one find it hard to swallow, a condition called âdysphagia.â As a result, they may not get enough nutrients. It's also risky if they accidentally inhale their food or drink, sending it down the wrong âpipeâ and making it hard to breathe. What helps: Part of the recovery from a stroke could include learning to swallow again. Small pieces of foods, or small sips of liquid, may help. Some people may need to be fed through a tube. What happens: Your kidneys filter waste out of your blood, and they prep it to send out of your body in urine. They also control your balance of fluids, sodium, and potassium, and make vitamin D, among other things. So when your kidneys don't work properly, it can cause many problems including high blood pressure, swelling and bloating, and blood or too much protein in the urine. What helps: Your doctor will tell you how to change your diet. If you're in the earlier stages of kidney disease, you may need to focus on sodium. If your disease is more advanced, you may also have limits on how much potassium or protein you can get. If you have kidney stones, you may need to make other changes to your eating habits. What happens: As dementia sets in, people with Alzheimer's may forget to eat, become overwhelmed by choosing and cooking food, or have trouble using utensils. As a result, they miss out on key nutrients and can lose weight they need to keep, becoming frail. They need to make sure they stay hydrated, as well. What helps: Offer lots of easy-to-eat foods, like smoothies and soups, so that the person you're caring for gets enough calories and stays hydrated. Try to limit distractions, and serve only one or two foods at a time. Remind the person that there's food in front of him or her. What happens: Anxiety can upset your stomach. If you're depressed, that can lead to eating too little or too much. What helps: Food, on its own, isn't a cure. But a balanced diet may help you feel better, and stomach symptoms often gradually fade as you start to benefit from psychological treatment in the form of therapy, lifestyle changes (like exercise), and medication, if needed. What happens: These conditions make the gastrointestinal ( GI) tract -- most commonly the intestines -- swollen and irritated. Symptoms often become worse over time and can include diarrhea, stomach cramps, loss of appetite, and nausea. So people often become cautious about what they eat. And if they limit their diet too much, they could miss out on nutrients and calories. What helps: You need medicine to control the symptoms and also to know what your triggers are, including which foods are irritating, so that you can avoid them. You'll want to work with your doctor, and write down your symptoms and what was going on right before they struck (including food and stress). A nutritionist who specializes in these conditions can also be a good resource. What happens: The symptoms of Parkinson's, which affects your body's nervous system, often get worse gradually, and can include constipation, feeling overly full after eating, and trouble swallowing. It can also affect the nerves that control your digestive system, causing a condition called gastroparesis (see above in " Diabetes"). What helps: Drink lots of water and eat fiber-rich foods to help keep yourself regular. Physical therapy and medications can improve your ability to chew and swallow. What happens: The virus can cause painful sores or infections inside your mouth or in your esophagus, making it difficult to swallow. Medications may also cause nausea and diarrhea, leaving you with little interest in eating. What helps: Your doctor may prescribe medication to boost your appetite, especially if you're losing weight. It also helps to stay hydrated, eat small meals, and avoid foods that cause bloating. Your doctor may recommend a special diet to make sure you get enough calories. What happens: Your thyroid doesn't make enough hormones to keep your body running properly. You might not have any appetite, yet still unexpectedly gain weight. It can also cause uncomfortable constipation. ( Hyperthyroidism, or overactive thyroid, can trigger the opposite symptoms: extreme hunger and thirst, diarrhea, and weight loss.) What helps: Treating the disorder with thyroid medication will usually reverse the symptoms and improve your appetite. What happens: This infectious disease commonly causes gastrointestinal symptoms such as bloating, weight loss, fatigue, and stomach discomfort. What helps: Avoid alcohol, try eating smaller, more frequent meals, and ask your doctor about medicine to fight nausea. There is a cure for hepatitis C, and for non-alcoholic fatty liver disease, the treatment is weight loss.